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Title: Spiders
Author: Warburton, Cecil
Language: English
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The Cambridge Manuals of Science and
Literature
SPIDERS
CAMBRIDGE UNIVERSITY PRESS
London: FETTER LANE, E.C.
C. F. CLAY, MANAGER
[Illustration]
Edinburgh: 100, PRINCES STREET
London: WILLIAM WESLEY & SON, 28, ESSEX STREET, STRAND
Berlin: A. ASHER AND CO.
Leipzig: F. A. BROCKHAUS
New York: G. P. PUTNAM’S SONS
Bombay and Calcutta: MACMILLAN AND CO., LTD.
_All rights reserved_
[Illustration: The Banana Spider, natural size, from a photograph by Mr
James Adams.]
SPIDERS
BY
CECIL WARBURTON, M.A.
Christ’s College
Zoologist to the Royal Agricultural
Society
Cambridge:
at the University Press
1912
[Illustration]
Cambridge:
PRINTED BY JOHN CLAY, M.A.
AT THE UNIVERSITY PRESS
_With the exception of the coat of arms at the foot, the design on
the title page is a reproduction of one used by the earliest known
Cambridge printer, John Siberch, 1521_
PREFACE
The modest dimensions of this book are perhaps sufficient indication
that it is not intended as an aid to the collector. There are about
five hundred and fifty known species of spiders in the United Kingdom
alone, and at least an equal number of pages would be needed to
describe them.
Our concern is with the habits and modes of life of spiders—especially
of such as are most frequently met with and most easily recognised, and
the reader, especially if he is fortunate enough to spend an occasional
holiday in southern Europe, will find little in the following pages
which he cannot verify—or disprove—by his own observations. Indeed
the hope that some of his readers may be induced to investigate on
their own account has actuated the writer throughout, and has led
him to lay considerable stress upon the methods of research and the
ingeniously devised experiments by means of which whatever knowledge we
possess has been obtained.
CECIL WARBURTON
CAMBRIDGE
_March, 1912_
CONTENTS
CHAP. PAGE
I. A Survey of the Field. Evidences of spider industry.
Where to look for spiders. Variety of habits 1
II. What is a Spider? The Arthropoda and their
divisions. Arachnida. Characteristics of a
spider. Spinnerets and their use 5
III. The Circular Snare. Foundation lines. The
spiral with its viscid beads. The building of
the snare. Why the spider is not caught in
its own snare 13
IV. The Mental Powers of Spiders. The human standpoint.
Instinct. Sight. Hearing. Smell.
Taste. Memory and “educability” 20
V. Trap-snares and Balloons. Variations of the
circular snare. The snare of _Hyptiotes_.
Webs of _Theridion_ and _Linyphia_. The iron
railing and its aeronauts. A race congress.
Gossamer. Geographical distribution 30
VI. _Agelena._ Its web. The spider and its behaviour
in captivity. The platform and its carpet.
The construction of the cocoon. Instinctive,
not intelligent 38
VII. Water-Spiders. Marine spiders. The fresh-water
spider. The diving bell, and how it
is filled with air. Behaviour of the male.
Winter and summer houses 47
VIII. Crab-Spiders.—Mimicry. The appearance of
crab-spiders. Their haunts. Protective
coloration and resemblance. Habits correlated
with structure. Probable origin of
“mimicry” 52
IX. Wolf-Spiders. General habits. Semi-aquatic
species. Nomads and settlers. Structure.
Eyes. _Lycosa picta._ A colony in full swing.
The burrow. Egg-bags. Recognition of
cocoons. Want of discrimination. The
Tarantula. Its haunts and habits. The
death-stroke. The burrow and its parapet.
Sunning the cocoon. Carrying the young.
Poisonous properties 58
X. Jumping Spiders. The Zebra Spider. Its structure.
Its wonderful eyes. Hunting its prey.
The use of the drag-line. Sight in jumping
spiders. Love dances. Sham-fights. A
remarkable piece of research 76
XI. Theraphosid Spiders. Sub-division of the Order.
Mandibles. _Atypus_ and its nest. Its habits.
Aviculariidae. A giant spider. Trap-door
nests. Method of burrowing. “Bird-eaters,”
and their habits. _Dugesiella._ Poor sight but
remarkable sense of touch. _Psalmopoeus_
in captivity 87
XII. Stridulation. How sound is produced in Arthropoda.
Its purposes. Popular mistakes.
Spines and Keys. The purring spider 105
XIII. The Spinning Apparatus. Spinnerets. Their
mobility. Spools and spigots. Glands. Arrangement
in _Epeira_. No interweaving of lines. Functions
of glands. Spinning operations.
The Cribellum. The feet of spiders 110
XIV. The Enemies of Spiders. Cannibalism. Egg
parasites. Moulting. Starvation. Body
parasites. Solitary wasps. A gruesome fate 120
XV. Concluding Reflexions. The “use” of spiders.
Wide range of habits. Complexity of instincts.
The mystery of the egg. The storage of
energy. Economy in diet. Conclusion 126
LITERATURE 133
INDEX 135
LIST OF ILLUSTRATIONS
_Frontispiece._ The Banana Spider.
FIG.
1. A Spider, a Mite and a Harvestman 9
2. The Garden-spider and its snare 15
3. Stretching the viscid line 19
4. Preparing for flight 35
5. _Agelena_ at work 44
6. A Crab-spider 53
7. Wolf-spiders 64
8. A Jumping Spider 77
9. The eyes of a Jumping Spider 78
10. The love dance 84
11. Stridulating “keys” 108
12. Spinnerets 114
13. Spiders’ feet 119
CHAPTER I
A SURVEY OF THE FIELD
There are certain days of the year when the immense wealth of spider
industry going on all around us is revealed in a way calculated to
strike even the least observant. We all know—and derive no peculiarly
pleasant thrill from the knowledge—that we can, if so minded, find
abundance of cobwebs and their occupants by visiting the cellar or the
tool-house; and probably we have all at times noticed, with a languid
interest, large circular webs on our favourite rose-bushes, with a
spider motionless in the centre.
But some spring or autumn morning, when the night has been foggy and
the sun has only just succeeded in dispersing the mists, every bush and
hedge is seen to be draped, every square foot of lawn and meadow to be
carpeted with spiders’ silk. There has been no special activity in the
domain of these creatures, but every silken line is beaded with drops
perhaps fifty times its diameter, and what yesterday required careful
observation to detect is now visible yards away, and we realise for
once something of the prodigious activity constantly going on though
ordinarily unnoted.
And it never entirely ceases. True hibernation, if it ever occurs, is
not the rule among spiders, and there is no time of the year when some
species may not be found at work. Beat trees or bushes over an old
umbrella, or sweep grass and herbage with a sweeping net in summer,
and you will never draw a blank—some spiders are sure to be found. In
winter such measures are profitless, but if you take the trouble to
grub among ground vegetation, or shake fallen leaves over a newspaper,
or search under stones or logs of wood you will have no difficulty in
finding spiders enough, and by no means dormant. I have even seen an
enthusiastic collector remove inches of snow and disinter rare species
from among the roots of the grass beneath!
Spiders, then, are plentiful enough, and it is not only individuals
that are numerous but there are vastly more kinds or species than
most people dream of. The Rev. O. Pickard-Cambridge, in a book under
the modest title of _The Spiders of Dorset_ indispensable to all
British collectors, quaintly observes that most of his friends claim
acquaintance with three kinds of spiders—the garden spider, the
harvest spider and the little red spider—two of which, as it happens,
are not spiders at all. Yet the British List contains about five
hundred and fifty species, and the spiders of the world, though only
very partially investigated, already include many thousands of known
and described forms.
In this little work we shall not at all consider the spider tribe from
the collector’s point of view. We shall concern ourselves rather with
habits and modes of life and such structural modifications as are
correlated therewith. Certain well-defined groups of spiders we shall
recognise, but specific names will interest us little. And we might do
worse than step out on such a spring morning as we have imagined and
rapidly survey the field which lies open for our investigation.
First, then, examine a little more closely one of the garden bushes
in which the spiders have been so busy, and the chances are that
three different types of snare will be readily distinguishable. There
are sure to be some of the familiar wheel-like snares of _Epeira_,
but note also the fine-spun hammocks of _Linyphia_ with stay-lines
above and below, and the irregular labyrinths of _Theridion_, its
lines crossing and recrossing without apparent method. These are
sedentary spiders, and always to be found at home. All spiders spin
for some purpose or other, but these—or at all events _Epeira_—have
brought the art to its highest perfection. Leave them for the present
and examine a sunny wall or fence. You may chance to see a little
zebra-striped, flat-bodied spider exploring the surface and directing
its opera-glass-like eyes in all directions in search of prey. This is
one of the Attidae or jumping spiders—few and sober-coloured in this
country, but extraordinarily abundant and often extremely beautiful in
tropical regions. Pause at the iron railing before leaving the garden
and observe how the topmost bar and the knobs which crown the uprights
are alive with spiders, mostly very small, and obviously of many
different kinds, extremely busy about something that it may be worth
while to investigate later; then go on into the lane, and note, in the
banks of the hedge-rows the great sheet-webs and tubes of _Agelena_,
a near relative of the house-spider, but with a cobweb, thanks to its
situation, comparatively free from accumulations of dust and filth.
The creatures skipping, dry-shod, on the surface of the river or
pond, though often called water-spiders, are true insects. The real
water-spider, _Argyroneta_, which, though air-breathing, spends most of
its time below the surface of the water, is not to be found everywhere,
but there are many riparian species which are semi-amphibious in their
habits and have no objection to a wetting.
Finally, turn into the wood and look carefully on the ground,
especially where last year’s leaves are still lying. You are certain
to see a few—and may very likely see countless myriads—of sober
coloured, rapidly moving “wolf-spiders” (Lycosidae), roaming in quest
of food. No stay-at-homes, these, but rovers, trusting to speed and
agility, and not to guile, for their food supply.
All the spiders we have observed so far are in active pursuit of their
daily business, but if we turn over stones, or logs, or look under
sheets of loose bark, we shall find others, quiescent for the moment,
but waiting for nightfall to begin their operations.
But we have probably seen enough to show that a pretty wide field for
investigation lies immediately at hand, and that a detailed study of
what we have cursorily glanced at will occupy us so long that we shall
have little time for considering the spiders of other lands. In the
first place, however, we had better make quite sure of what is meant by
a spider.
CHAPTER II
WHAT IS A SPIDER?
Not many years ago the group Insecta was held even by Zoologists
to include numberless small creatures—centipedes, spiders, mites,
etc.—which further study has shown to present essential differences
of structure, and in popular language any fairly minute animal is
still an insect, just as any insect is popularly a “fly”—or, in the
United States, a “bug.” Scientifically the use of the term Insect is
now much restricted, though still extensive enough in all conscience,
since it includes many more than a quarter of a million known species.
Zoologists recognise a large group of animals characterised by having
no internal skeleton but a more or less firm external coating of a
peculiar substance called _chitin_, often strengthened by calcareous
deposits, which necessitates the presence of joints in their bodies,
and especially in their limbs if they are to move freely, just as
medieval suits of armour required to be jointed. These are the
Arthropoda. One subdivision of this group consists of aquatic animals,
breathing by gills, and known as Crustacea. Crabs, lobsters, shrimps
and “water-fleas” are familiar examples, and with the exception of the
so-called land-crabs the only Crustaceans habitually found on land are
wood-lice.
The other Arthropoda are air-breathing, and since their characteristic
breathing organs are branching tubes known as _tracheae_, the term
Tracheata is sometimes used to include them all. They fall naturally
into three divisions, the Myriapoda, the Insecta and the Arachnida, and
it is in this last-named division that we shall find the spiders.
The Myriapoda are the centipedes and millipedes, and having said this
we may dismiss them, for insects and arachnids are strictly limited as
to legs; and no myriapod can ever be mistaken for a spider.
The Arachnida are so varied in structure that it is not easy to give
characteristics common to them all, and to any general statement there
are bound to be exceptions, but for practical purposes it may be said
that while an insect, when mature, has only six legs, and a pair of
feelers or antennae of quite different structure, Arachnids have
normally eight legs, and their feeling organs are not antennae but
leg-like “pedipalps.”
Most insects are distinguishable at once by the possession of wings,
which are never found among the Arachnida, and they generally undergo
a marked transformation or metamorphosis in their progress from the
egg to maturity, taking on at first the form of a caterpillar or grub
and then that of a chrysalis; but as there are many wingless insects
and many in which the metamorphosis is very slight, the test supplied
by these characteristics is only of partial application, and we shall
do better to rely on the number of legs, and the nature of the feeling
organs. If, therefore, we find a small wingless animal with eight legs
and a pair of feelers which are not thread-like but much of the same
character as the legs, though not used for locomotion, we may be sure
that we are concerned with an Arachnid.
But is it a spider?
Now some groups of the Arachnida may be put out of court at once
as having an appearance so characteristic that no confusion is
possible. Such are the Scorpions, and the minute Chernetidea or “False
Scorpions,” but this cannot be said of the Phalangidea or “harvestmen”
or of the Acarina or “Mites,” members of which groups not only may be,
but frequently are popularly taken for spiders. In fact the Phalangidea
are very commonly spoken of as “harvest spiders” and the “red spider”
is a mite. A very brief inspection, however, with a pocket lens will
settle the matter without the least difficulty.
A spider’s body consists of two parts, a cephalothorax (head + thorax)
and an abdomen. There is a waist, but no neck. The eight legs are
attached to the cephalothorax, and the abdomen is not segmented or
ringed like that of an insect, but entire, and bears at its extremity
or on its under surface a little group of spinnerets or finger-like
projections from which the spider’s silk proceeds. For the moment these
three characteristics will suffice—the “waist” behind the leg-bearing
portion of the body, the unsegmented, legless, abdomen, and the
spinnerets (fig. 1 _B_). A harvestman, for instance, lacks the waist,
and its abdomen is segmented. Mites are of very varied form and in
some the body is more or less divided into two portions, but at least
two pairs of legs will be found to be attached to the hinder portion;
and neither harvestmen nor mites possess the spinnerets which are
the most striking characteristic of the spider; some mites—like the
“red spider”—can spin, but the mechanism by which that operation is
performed is of quite a different nature.
[Illustration: Fig. 1. _A_, a Mite; _B_, a Spider; _C_, a Phalangid.]
Having, then, very readily determined our specimen to be a true spider,
we may as well use it to note some further structural points the
detailed examination of which may be deferred till we have considered
their functions. Note the jaws or _chelicerae_, consisting of a stout
basal part and a fang which, when not in use, is shut down like the
blade of a knife; note the pedipalps or feelers, exactly like small
legs, but showing by their action that their function is sensory and
not locomotor. If they are knobbed at the end, the specimen is a male,
otherwise it is a female or as yet immature. Look closely at the front
part of the cephalothorax, and several eyes will be visible—probably
eight. They are not compound—divided into innumerable facets, like
those of insects—but simple and smooth, though to make sure of this
the use of a microscope would be necessary. Finally, obtain a view of
the under surface of the abdomen, and note in front, on either side of
the middle line, two semilunar patches of a lighter colour. These are
the “lung-books,”—special breathing organs peculiar to these animals;
two is the usual number, though certain spiders possess a second pair
behind the first.
But the spinning mammillae or spinnerets are still more characteristic
and more easily seen, though, curiously enough, it is not among the
cleverest spinners that they are most conspicuous. In the family
to which most of the cellar spiders belong (Agelenidae) and in the
elongate brown or mouse-coloured spiders found lurking under stones
(Drassidae) they are visible as little finger-like projections at the
posterior end of the abdomen, but if we have taken our specimen from a
circular web (Epeiridae) we shall have to look for them more closely.
In these spiders they are beneath the abdomen near its termination,
and are not visible from above. Moreover when at rest their tips are
applied together so that they form a small rosette in surface-view, or,
in profile, a slight cone.
The best way to capture a spider for examination is to induce it to
run up into a small glass specimen tube—for spiders readily part with
their legs if handled roughly—and if we have adopted this method we
shall see the spinnerets in use as the animal crawls about the tube. It
will not move without first attaching a silken cable to the glass, and
this cable lengthens as the spider progresses, so that before long the
interior of the tube will be a network of silken threads, and its sides
will be flecked with little white specks where the threads have been
re-attached for a new departure; and by observing closely we shall be
able to note the extreme mobility of the spinnerets in action.
All spiders spin, but it is by no means all spiders that make snares
for the purpose of catching prey. The fundamental purpose of the
spinning organs seems to be to connect the spider with its point of
departure. The jumping spiders (Attidae) make no snare, but this
“drag-line” as it has been called comes in very useful when stalking
prey on the vertical surface of a wall, when a miscalculation at the
moment of pouncing upon it would entail a considerable fall were it not
for such an anchorage. It can hardly be doubted—though of course it is
incapable of proof—that all the more complicated spinning operations
originated in this universal spider habit, but all known spiders have
learnt to apply their power of making silk to other purposes. If they
do not make snares they at least spin “cocoons” for the protection of
their eggs, and if they have a definite home from which they emerge
to seek food, such a retreat is always more or less lined with silk.
It is clear that a spider cocoon is quite different from that of an
insect; it encloses the eggs and is manufactured by the mother, whereas
among the insects the larva makes the cocoon for the protection of the
pupa or chrysalis into which it is about to turn. However far from
exhaustive the foregoing study of spider structure may be it will
suffice for our purposes, at least for the present, and we may proceed
at once to an investigation of one of the most remarkable achievements
in the way of spinning—the familiar circular snare or wheel-web of the
garden spider.
CHAPTER III
THE CIRCULAR SNARE
Select the most perfect circular snare at hand, and examine it
attentively. In the autumn, when the large garden-spider, _Epeira
diademata_ (fig. 2 _A_), is mature, it will probably be easy to find
such a snare a foot or more in diameter. It is stretched within an
irregular frame of _foundation lines_ of extra thickness and strength,
and consists of a large number of radii or spokes connected by what
appear to be a series of concentric circles, in reality a continuous
spiral, like the hair-spring of a watch. The central portion is
different from the rest of the wheel. Probably in the very centre
there is a vacant space and round this a hub, consisting of a spiral
line different in appearance from that of the main spiral. It does
not leave a radius exactly at the point where it strikes it, and the
rather zig-zag effect has caused it to be known as the “notched zone.”
Touch the web and it adheres to the finger, but all its lines are
not adhesive. Test this with some fine-pointed implement, and the
foundation lines, the radii and the notched zone will give negative
results; the spiral line alone is viscid, and its viscidity is due
to the presence of thousands of little beads of gummy matter strung
on a thin elastic thread. The vast number and uniformity of these
beads—estimated at 120,000 on a large web—excited the wonder and
admiration of naturalists until it was proved that they were not
deposited by the spider as beads at all, but as a uniform coating of
viscid matter which subsequently arranged itself into equidistant
globules easily explicable by the physicist. Indeed precisely the same
phenomenon is seen on a dew-laden web, where similar but very much
larger beads of water decorate all the lines.
From the hub of the wheel we shall very likely notice a rather stout
cable diverging from the plane of the snare and leading to a nest of
leaves spun together. Here the spider is to be found when not on duty
in the centre of the wheel, and here it constructs its egg-cocoons.
This, then, is the complete circular snare, but we shall understand it
much better if we watch the spider at work in its construction.
[Illustration: Fig. 2. _A_, the Garden Spider. _B_, diagram of a sector
of the snare. _f_, foundation line; _r_, radius; _v.s_, viscid spiral;
_n.z_, notched zone; _h_, hub.]
The first business of the spider is to lay down the foundation lines.
Any sort of trapezium—or even a triangle if large enough—in a more
or less vertical plane will suffice, and under some circumstances
the operation is simple enough. The spider attaches a line at the
point of departure and crawls along, spinning as it goes and holding
up the newly-spun thread by the claws of one of its hind feet, till
it reaches a suitable spot for its farthest limit. It then hauls in
the slack and makes it fast. It will probably return along the line
thus laid down—still spinning—to the starting point, thus doubling
the strength of the cable, and indeed a large spider will often repeat
this operation several times. Now the upper boundary of the future web
is secured. It is next necessary to find points of attachment for the
lower boundary, and the spider either drops or climbs down—always
carrying a line—from one of the ends of the upper line till it reaches
a spot suitable for its purpose, and the previous performance is
repeated. If there is any difficulty about a fourth attachment it is
always open to the spider to climb back along the two lines already
laid down, and by carrying a loose line with it, to secure at all
events a triangular frame-work. This frame-work, whether trapezoid
or triangular, will be reinforced several times and made thoroughly
trustworthy before the work of making the actual snare is proceeded
with.
Now the foregoing operation is obviously perfectly simple in certain
cases, as, for instance when a spider has chosen lattice work, or the
mouth of an empty barrel as its “pitch,” but snares may easily be
found in situations where such a mode of procedure seems impossible.
In a pine forest, for example, one may see huge webs stretched at a
great height from the ground between boles ten feet apart; or one may
find such a snare spread across a stream at a spot where the trees on
either side do not intermingle their boughs. How in such cases does the
spider accomplish its purpose?
There is little doubt that, wherever practicable, the spider walks
round, sometimes crawling quite an astounding distance, but that it can
at need, resort to another method, is easily proved by a very simple
experiment in the house. Fill any vessel—a basin or a bath—with water
and arrange an upright post in the middle, placing a spider upon it.
If the air in the room is absolutely still the captive is powerless to
escape, but if draughts are present it will sooner or later disappear;
and it accomplishes this feat by emitting a thread which, caught by the
air-current, is drawn out from its spinnerets till it by and by becomes
entangled in the surrounding furniture. This power of emitting silk to
some little distance and allowing the wind to draw it out is, as we
shall see, frequently exercised in the early life of many spiders.
The foundation lines which may thus have given the spider great trouble
to secure, are of extreme importance to it, and may serve for several
snares in succession. There is little hesitation or delay about the
subsequent operations. The spokes of the wheel are readily formed by
carrying lines across to opposite points of the frame-work and uniting
them where they intersect. They are laid down in no special order, but
more or less alternation is generally noticeable—apparently for the
purpose of keeping the tension equally balanced—and the spider will
occasionally desist in order to go and brace up the frame-work with
additional stays, which generally have the effect of converting it to a
polygon.
Before long the requisite number of fairly equidistant “spokes” or
radii are visible, and then the spider, starting from the centre,
rapidly spins a spiral thread consisting of a few coils only, to the
circumference, stepping from spoke to spoke. This is only a temporary
scaffolding and will not be suffered to remain in the completed snare.
If the structure is touched at this stage of the operations it does not
adhere to the finger; the viscid spiral remains to be laid down. Though
it does not hesitate for a moment, the spider now works with a peculiar
deliberation, but the operation will be much better understood by
actual observation than by any amount of description, and we shall only
recommend the reader to note that the new spiral is exceedingly elastic
and that at the moment of its attachment to a spoke it is stretched
and let go like the string of a bow. The spider seems carefully to
avoid treading on it as it proceeds, utilising the non-viscid spiral
scaffolding already described.
[Illustration: Fig. 3. Stretching the viscid spiral.]
A little attention to the centre of the wheel, and the snare is
complete. Some species of _Epeira_ entirely remove the centre, leaving
a circular empty space, while others fill it with an irregular network
of threads.
How does the garden spider avoid getting caught in its own web? We have
shown that there are many lines which are not viscid, and no doubt
these are utilised as far as possible, but it can hardly happen that
the spider never touches adhesive portions of the web with legs or body.
Possibly some explanation is furnished by an ingenious experiment
which Fabre performed. He found that a glass rod, lightly smeared with
oil, did not adhere to the viscid spiral; neither did a leg freshly
taken from a garden-spider unless allowed to remain in contact for
a considerable time. When, however, this leg had been washed with
bisulphide of carbon, which dissolves any kind of oily substance, it
adhered at once. It would seem likely, therefore, that the legs and
body of the spider itself are protected by some oily exudation from any
danger of adherence to its own lines.
CHAPTER IV
MENTAL POWERS OF SPIDERS
Before leaving the garden-spider let us undertake some little
investigation of its mental powers—if it possesses any. The commonest
mistake with regard to all animals is to interpret their actions
from the human standpoint, and to credit them with emotions and
with deliberate forethought of which there is in reality no proof
whatever. The power to spin such a complicated snare as we have just
described predisposes us to attribute a high order of intelligence to
a creature capable of such an achievement, and when it “shams death”
on being disturbed we immediately pronounce it “cunning.” The wildest
conclusions are sometimes arrived at. One author, for instance, states
that he has seen an Attid spider “instructing its young ones how to
hunt” and adds that “whenever an old one missed its leap, it would
run from the place and hide itself in some crevice as if ashamed
of its mismanagement.” Such inferences, of course, were entirely
unwarranted from the facts observed. Now the fact that a newly-hatched
garden-spider can make a complete snare without ever having seen the
operation performed immediately relegates that action to the realm of
instinct,—not less wonderful than intelligence perhaps, but certainly
quite distinct from it. With the much discussed origin of instinct we
are not here concerned, but a pure instinct differs from intelligence
in this: that it is due to inherited nervous mechanism and results in
actions the object of which may be quite unknown to the actors. There
is no conscious adaptation of means to an end. When a young spider
spins a web there is not only no evidence that it does so with the
deliberate purpose of catching flies, but many known facts go to prove
that it performs the feat, “because it feels as if it must,” and is
quite ignorant of the purpose to be subserved.
It is no doubt quite beyond our power to ascertain accurately the
mental condition of a spider, but it is perfectly easy to make a few
illuminating experiments on two points which have a very decided
bearing on intelligence:—the development of the senses, and the degree
of what has been called _educability_, or the power of learning from
experience. To what extent can the spider see, hear, smell, feel,
taste? How far is it capable of varying its action as the result of
experience? The senses, as far as we know, are the principal—if not
the only—avenues by which external impressions can reach the seat of
intelligence, and there is no surer indication of the intelligence of
an animal than the degree to which it is susceptible of education.
Probably most readers know the immortal story of the pike cited by
Darwin in the _Descent of Man_. The pike was in an aquarium, separated
by a sheet of glass from a tank in which were numerous small fish.
Not till three months had expired did the pike cease to dash itself
against the glass partition in its attempts to seize the fish in
the neighbouring tank. It then desisted and had evidently learnt
something—but what? After three months, the glass partition was
removed, but the pike refused to attack those particular fish, though
it immediately seized any new specimens introduced to the tank. All
that it had apparently learnt was that an attack on a particular fish
resulted in a violent blow on the nose. Some degree of intelligence
must be conceded to the pike, but it can hardly be considered of a high
order.
Now the garden-spider possesses eight eyes, and might be expected
to see fairly well, but the experimenter will very soon come to the
conclusion that the habitual use it makes of them—at all events in
day-light—is very slight. Touch a web with a vibrating tuning-fork
and the spider will rush to the spot and investigate the instrument
with its fore-legs before distinguishing it from a fly. Remember,
however, that this is only true of what are sometimes called sedentary
spiders; species which hunt their prey have much better vision. Yet
even among sedentary spiders the power of sight is not negligible, for
a most trustworthy observer states that he has several times seen _Meta
segmentata_, a very common small Epeirid, drop from its web to secure
an insect on the ground beneath, and return with it by way of the drop
line, and the same action has been observed in the case of _Theridion_,
which spins an irregular snare.
There are peculiar difficulties attending experiments on the subject
of hearing. An absolutely deaf person may be aware of the sounding
of a deep organ note through the sense of feeling, and a well-known
experimenter was on the point of drawing interesting conclusions from
the behaviour of a spider in response to the notes of a flute, when
he found that precisely the same results were obtained by a soundless
puff of air. It seems hardly possible to make sure, in the case of a
spider in a snare, that the sound vibrations are not _felt_, apart from
any sense of hearing, and it is a remarkable fact that it is only the
snare-spinning spiders that make any response to sounds:—free-roving
spiders are apparently quite deaf.
In experimenting with sound we must take two precautions: the
instrument used must not necessitate any marked action which may be
visible to the spider, nor must it give rise to palpable air-currents.
These requirements are best met by a tuning-fork of not too low a
pitch. We cannot _feel_ the air vibrations emanating from it, but
can only perceive them by the ear, but we have no proof that the
spider’s sense of touch ceases precisely at the same point as our own.
However, no better instrument for experiment seems to be available, so
we take a tuning-fork, and approach it cautiously—in the quiescent
state—towards the spider, stationed, we will suppose, in the centre
of its snare. No notice is taken, and we carefully withdraw it, set
it vibrating, and approach it again in the same manner. There is now
generally a response, the spider raising its front legs and extending
them in the direction of the fork, or, if the sound is loud, dropping
suddenly by a thread and remaining suspended some inches below the
snare. The experiment should be repeated several times with the fork
sometimes still, sometimes vibrating, and the conclusion arrived at
will be that the spider is aware of the vibrating fork—but by which
sense? It is noteworthy that a fork giving a low note is always most
effective.
Now here is a very remarkable fact. In two widely different groups of
spiders—the Theraphosidae or so called “bird-eating spiders” and the
Theridiidae—there are species with a stridulating or sound-making
apparatus, and we should hardly expect a deaf creature to evolve an
elaborate mechanism for the production of sound. This is a matter,
however, that we shall discuss later.
No amount of research has succeeded in localising the sense of hearing
in spiders, supposing it to exist. The creature may lose any of its
five pairs of limbs (four pairs of legs and one pair of pedipalps)
without alteration in its response to sound. If the front legs
are missing the second pair are raised when the vibrating fork is
approached.
It is fairly easy to test the sense of smell in these creatures, the
only necessary precaution being that no acid or pungent substances
capable of having an irritating effect on the skin, such as vinegar or
ammonia, must be employed. Such perfumes as lavender or heliotrope
are free from this defect. Take a clean glass rod and present it to
the spider as before, and no notice is taken. Now dip it in oil of
lavender, allow it to dry, and present it again. Most spiders respond
to such a test, Epeirids generally raising the abdomen, and rubbing one
or other of the legs against the jaws, while jumping spiders generally
raise the head and back away from the rod. Different essences produce
different effects, but there is seldom any doubt that the creature is
aware of their presence; it is not deficient in the sense of smell, but
its localisation has hitherto baffled research.
The sense of taste does not seem to have been made the subject of any
definite experiments among spiders, though such experiments might well
lead to interesting conclusions, and the reader might do worse than
undertake some on his own account. It would be easy, for instance,
to supply a garden-spider with various insects which are generally
rejected by other insectivorous animals, and to note its behaviour. It
might refuse to have anything to do with them, or it might sample them
and turn away in disgust. In the first case the explanation might be
that it was warned of their probably evil taste by their coloration
or smell, but in any case here is an interesting little field for
research. It is the general belief among arachnologists that the sense
of taste is well developed among spiders, and it is highly improbable
that a sense so necessary for the discrimination of suitable food
should be lacking in animals with so respectable a sensory equipment.
There is no doubt at all that the sense of touch is extremely well
developed in spiders, especially perhaps, in the sedentary groups, and
it is probable that, under ordinary circumstances, the garden-spider
works almost entirely by its guidance. Whether in the centre of the
web or in its retreat under a neighbouring leaf it is in direct
communication with every part of its snare by silken lines, and the
least disturbance usually suffices to bring it to the spot; and then,
as we have said, it will generally touch the disturbing object, however
unpromising in appearance, before deciding on its line of action. There
is little doubt that many of the numerous hairs and bristles with which
its limbs are furnished are distinctly sensory in function.
So much, then, as to the senses of spiders; but what about their
“educability”—their power of learning from experience? Here is
evidently a wide subject, and a difficult one full of pit-falls for
the unwary, but we may nevertheless draw some inferences from the
quite elementary experiments on the senses which have been outlined
above. A spider drops on account of the sounding of the tuning-fork in
its neighbourhood; can it be educated to take no notice of the sound
after repeatedly finding that no evil consequences follow? It will
perhaps be most instructive to give in a condensed form the results
of an actual experiment selected from many performed by two American
arachnologists, George and Elizabeth Peckham, whose researches have
thrown more light than any others upon the mental equipment of spiders.
They had an individual of the small Epeirid species _Cyclosa conica_
under observation for a month, and tested it almost daily with the
tuning-fork. At the sound of the fork the spider would drop; when
it had recovered itself and returned to the snare the fork would be
sounded again, and so on. Now on July 20 the spider fell nine times
successively—the last three times only an inch or two—and then
took no further notice of the vibrating fork. On subsequent days,
until August 5, she fell either five, six or seven times, except on
two occasions when a day’s test had been omitted, and then eleven
successive falls occurred before the spider ceased to respond. On
August 5 she seemed startled at the sound but did not fall, though the
fork was sounded nine times. During the remainder of the experiment she
generally remained perfectly indifferent to the fork, though on one or
two occasions she partially forgot her lesson and dropped a very short
distance, immediately recovering herself.
Observe that the basis of educability is memory. For a fortnight, in
the case of this particular spider, the lesson learnt on one day
seemed to be entirely forgotten the next morning, but thereafter a
definite change of habit seemed to result. This does not appear a very
great intellectual achievement, but it is by no means despicable,
for it must be borne in mind that the habit of dropping when alarmed
is almost the only means of defence such a spider possesses, and the
instinct which prompts it must be very strongly ingrained. In the
words of the experimenters—“Taking this into consideration, it seems
remarkable that one of them should so soon have learned the sound of
the vibrating fork, and should have modified her action accordingly.”
This single experiment has been here described in some detail largely
for the purpose of impressing the reader with the importance of
reducing the problem to its simplest terms before any inferences are
drawn, and it may well act as a model for any which he may be inclined
to undertake on his own account. The more complicated the action,
the more likely is the experimenter to read into it motives and
mental operations which exist only in his own imagination, and with
this warning we must take leave of a subject which might tempt us to
encroach too much on an allotted space.
CHAPTER V
TRAP-SNARES AND BALLOONS
There are some interesting variants of the circular snare spun by some
exotic Epeirids. One North American species spins it in a horizontal
position and then raises the centre, and, by an elaborate system of
stay lines from above, converts it into a very accurately shaped dome.
A whole group of orb-weavers habitually decorate a sector of the snare
with bands of flocculent silk, the object of which for a long time
puzzled arachnologists, till it was observed that the spider drew upon
this reserve supply of material to wrap up particularly obstreperous
insects. It is not unusual for a spider of one of the common species to
remove a whole sector of the snare, and by stretching a line from the
centre to a place of retreat along the gap thus formed, to provide an
unencumbered avenue between its home and its post when on duty. For it
must not be forgotten that a spider has to walk warily on its own web,
and must avoid, as far as possible, treading on the adhesive lines, or
delay and damage to the structure are sure to ensue.
As a rule the circular snares of the different British species are of
a very uniform pattern, differing chiefly in the degree of neatness
with which they are constructed, and in certain minor details of the
“hub,” but we have one spider, _Hyptiotes paradoxus_—an exceedingly
rare species, scarcely ever seen beyond the limits of the New
Forest—which makes such a strange snare that it seems a pity to omit
all mention of it. It consists of a sector—about one sixth of the full
circle—comprising about four radii with cross lines. From the point
where the radii meet, a “trap-line” connects the sector to another
point of attachment; on, or rather under, this trap-line, the spider
takes up its position, hauling it in so as to tighten the web and to
leave a slack portion of the line between the points where it holds
on by its front and hind legs. When an insect impinges on the web and
causes it to tremble, the spider immediately lets go with its fore
legs, and the consequent vibration of the web helps to entangle its
prey.
The circular snare is the highest form of spinning work attained by
spiders, and there is little temptation to expend much time in studying
the cruder structures that meet the eye everywhere, but two other types
are worth a brief notice. Examine any garden bush—particularly a
holly bush, of which the rather rigid leaves provide excellent points
of support—and you will find numberless small webs made without any
discoverable method, the lines crossing one another at random in all
directions. These are the snares of some species of _Theridion_, and if
the webs lack interest the spiders themselves are worth looking at, for
they are nearly always quite prettily ornamented.
The other common type of snare is that of _Linyphia_. It is larger and
of more definite design, consisting of a finely-spun hammock stretched
horizontally, and surmounted by a labyrinth of irregular lines. Flies
entangled in the labyrinth fall upon the hammock in their struggles to
escape, and the spider is at hand—always on the under surface of the
hammock—to ensure their capture.
Having noted these three common types of snare, let us leave the garden
and choose a new field for our observations.
If it is an absolutely calm sunny October morning it will be a suitable
occasion for visiting an iron railing, the “knobbier” the better. Early
summer will do, but late autumn is generally more fruitful. Almost
any railing will serve, but the most satisfactory kind is one with
the uprights surmounted by round knobs, and not by spikes. We see at
once that the knobs, and the upper rail are glistening with silken
lines; many spiders have obviously been at work there. Lines streak
the top-rail in all directions, stretch from knob to rail, or from
knob to knob if not too distant, while here and there loose ends or
streamers flutter gently in the slight currents of air. And closer
inspection reveals various small objects moving among this labyrinth
of threads. Most of them are spiders, though insects, and particularly
weevils, are not wanting. No doubt the weevils know their own business,
though the writer has not been taken into their confidence, but the
spiders are the particular object of our investigation. And first of
all note that it is a veritable race-congress of spiders; the most
varied groups are represented. Wolf-spiders (Lycosidae) which under
ordinary circumstances rarely leave the ground are found in company
with crab-spiders (Thomisidae), jumping spiders (Attidae), as well as
Epeiridae and Theridiidae of which we already know something. They
have only one thing in common—they are either small species or small
and immature specimens of larger species. They seem to be scrambling
about in a meaningless sort of way, paying little or no attention to
each other—which is odd, for spiders are terrible cannibals, and as a
general thing it would be exceedingly unsafe for a small spider to rub
shoulders with a larger one of a different species.
The majority of them are very small, more or less black, Theridiid
spiders, the “micros” of the tribe, and their proper home is among
the roots of grass and herbage. Many of these are interesting objects
for the microscope—especially if males—because of the remarkable
protuberances or turrets which rise from their heads and bear their
eyes as on a watch tower.
These spiders are clearly not “out” for food; they have left their
ordinary beat for quite another purpose, and we shall probably not
have to wait long before discovering it. Some one of the group ceases
its apparently purposeless wandering, and, turning its head in the
direction of what slight wind there is, raises its fore-body to the
full extent of its straightened legs, and elevates its abdomen to the
utmost. Now watch closely—using a handglass if you have one—and you
will see streamers of silk proceeding from its spinnerets. They are
shot out for a short distance and then the air current draws them out
further till they often extend for several feet, though their extreme
fineness makes it almost impossible to form an accurate judgment of
their length. Meanwhile the spider has not merely been standing on its
“toes,”—it has been firmly gripping the silken lines on the railings
with its claws. Soon it feels the pull of the streaming threads,
and when the tension is sufficient it lets go with all its claws
simultaneously, vaults into the air and sails away. Sometimes a start
is made prematurely and the insufficient buoyancy of the streamers
causes the spider to descend almost at once, and a new start is made.
[Illustration: Fig. 4. Young spider preparing for an aerial voyage.]
This, then, is the habitual method by which new broods of spiders
distribute themselves, especially the sedentary kinds which would
otherwise soon become over crowded in the neighbourhood of the parent
nest. And we really need not have sought out a railing at all except
for its very great convenience of observation. The same thing is going
on everywhere. It largely accounts for the astonishing carpet of silk
that the dew reveals to us on lawns and meadows at such times of the
year. Young spiders have been busy from early dawn crawling over the
grass, climbing the higher blades, and setting sail, and the whole
field is covered with their lines. Railings come in handy as furnishing
an elevated starting point, but any shrub or bush will do, and young
spiders have been seen setting sail from the parent web itself.
McCook has given some interesting notes of his own observations on
aeronautic spiders. He followed an Attid spider fifty feet till it was
carried upward out of sight in a current of air. A Lycosid disappeared
in the same way after being followed—at a run—for a hundred feet. The
largest Epeirid he ever saw taking flight was “the size of a marrowfat
pea, say one-fourth of an inch long. After having floated over a field
and above a hedge-row, it crossed a road and anchored upon the top of
a young tree.” But perhaps his most interesting observation was on the
ability of spiders to control in some measure the duration of their
flight by reefing their sails if they wish to descend, for he saw a
ballooning spider collecting some of the streamers into a ball of silk
which accumulated near its mouth as it gradually sank to earth.
The phenomenon known as “gossamer” has puzzled people for centuries,
and English poetical literature is full of allusions to it. Chaucer
classes it with “ebbe and floud” as an unsolved riddle, and Spenser,
Quarles and Thomson all make mention of it, generally embodying the
popular belief that it somehow had its origin in dew. “Scorchèd deaw”
Spenser calls it, while Thomson’s expression is “dew evaporate.” The
phenomenon in question is the occasional appearance of vast numbers of
silken flakes which fill the air, and which in some recorded instances
extend over many square miles and to a height of several hundred feet.
Our observations will have given a clue to its origin which is entirely
attributable to spiders, and in large measure to their ballooning
habit, though no doubt reinforced by a large quantity of silk spun
for other purposes and caught up into the air by the breeze. For a
vivid account of such a shower the reader is referred to Letter LXV of
White’s _Natural History of Selborne_, and Darwin in his _Naturalist’s
Voyage_ (Chap. VIII) records a case of the “gossamer spider” descending
in multitudes on the “Beagle” when sixty miles from land.
In the ballooning habit we have the probable explanation of the
wide distribution of certain species of spiders which seem at first
exceedingly ill adapted for covering large distances. The Huntsman
Spider, _Heteropoda venatorius_, is practically cosmopolitan in
tropical and sub-tropical regions and the usual view has been that
ships have conveyed it from port to port. McCook, however, gives
several reasons for believing that the trade winds have much more to do
with the matter, and this may well be the case, though both agencies
have doubtless been at work.
Very likely it was not obvious to the reader why he was recommended to
select a particularly calm, sunny autumn day for his study of spider
aeronautics; a strong steady breeze might well appear more suitable for
the purpose. Yet he would find these operations at a standstill on a
windy day, and the best possible conditions are a still warm morning
after a spell of cooler weather. The lightest air-currents serve to
float the delicate silken threads, and, what is more important, the
increase of temperature causes an upward draught which rapidly carries
the spider to a useful height where it sails gently away instead of
being swept roughly over the surface of the ground.
CHAPTER VI
AGELENA
Before going farther afield, let us investigate one of the spinners
of the sheet-webs that are so unpleasantly familiar in the house. We
object to them on very obvious grounds, first as evidence of neglect
and bad housewifery, and secondly as repulsive objects when covered by
accumulations of dust which their firm texture and their durability
make inevitable.
The common house-spiders belong to the family Agelenidae. It is quite
likely that their original home was in a warmer climate where they
lived out of doors, but that was long ago, and now they uniformly
select buildings of some sort for their operations. They have, however,
even in this country, several open-air cousins, and most people know
the great sheet-web spider of the hedge-rows, though its name—_Agelena
labyrinthica_—may be new to them. Its web consists of a closely woven
wide-spreading sheet connected with a tube of even denser material, in
the mouth of which the spider may generally be seen lurking, a rather
sinister object. If a better view of the animal is desired it is only
necessary to agitate the web slightly and the spider runs forward to
investigate. It is a large species as British spiders go—about three
quarters of an inch in length—with the abdomen rather prettily marked
with oblique white streaks.
It is very unlike our garden spider in certain points of structure;
its body is more elongate and rather rigid, with little play of action
between the cephalothorax and the abdomen; its legs are notably long,
and so are two of its spinnerets, which can be seen protruding beyond
the abdomen as we look down upon it.
But we shall gain little information by looking at the completed
web, and our best plan is to take the animal home and observe it
in captivity. We have prepared for its reception a box about a foot
square, with a gauze top and a movable glass front.
It is not such an easy matter to secure the spider, which can run like
a lamp-lighter, and which has a way of escape at the lower end of its
tube. The safest way is suddenly to shut off this means of retreat with
the finger and thumb of the left hand and simultaneously to present a
glass phial at the mouth of the tube; the spider runs up into it and
is taken without the risk of injury. It is never advisable to handle
spiders, not because any British species is formidable, but because
they so readily part with their limbs in order to escape, and the
chances are that only a mutilated specimen will be obtained.
Now _Agelena_ does not seem to be a particularly engaging pet, but
it has its points. In the first place, it very quickly makes itself
at home; a short time is spent in exploring its new quarters, but it
adapts itself almost at once to its changed situation. Moreover it
is of a peaceable and domestic disposition and the male and female
live amicably together, which is far from being the case among
the Epeiridae, whose peculiar marital relations are often—quite
wrongly—attributed to the whole tribe of spiders. A male garden-spider
courts the female at the risk of his life, and it is not surprising
that he should evince great hesitation and caution in his advances. If
his attentions are unwelcome, or even if they have been accepted, he
will be promptly trussed up and eaten unless he beats a hasty retreat.
But with _Agelena_ the conjugal relations are exemplary, and harmony
reigns in the home. The question of food is certainly a difficulty,
but if insects are let loose in the cage the spider will attend to the
catching of them. In some cases raw meat has been found a satisfactory
substitute.
After a brief exploration of the box the captive soon becomes busy,
going to and fro across its cage and attaching lines to the sides at
some height up from the floor. So fine is the work that for a long
time hardly anything is visible, and the movements of the animal are
the only clue to what is taking place. By and by it becomes evident
that a sort of skeleton platform has been spun across the box, upon
which the spider is able to walk. It is continually strengthened by
new threads, and braced by stay-lines above and below. It has been
hardly possible to follow the operations by which this has come about,
and even now we are chiefly aware of the existence of the platform
because we see the spider walking upon it; its movements seemed very
scrambling and unmethodical, but they have resulted in the foundation
of the sheet-web and its terminal tube. But now it begins to behave
quite differently, and another phase of the work has clearly begun;
it crawls about over the almost invisible foundation lines with a most
curious gait, using its long legs to sway its body from side to side,
raising and depressing its abdomen at intervals, and as this motion
continues a beautiful gauzy sheet of incredibly fine texture gradually
grows into view. What is happening is that the spider is strewing over
the foundation lines multitudinous threads from its long posterior
spinnerets, which are beset on their under surface with numbers of
hair-like spinning tubes from each of which the silk is issuing. All
day long the process goes on, and by slow degrees the web increases in
density. Indeed for days after the structure is complete the spider
spends odd moments in going over the ground again till the sheet, and
especially the tube proceeding from it to a corner of the box, are so
closely woven as to have become almost opaque, and its occupant at
length appears to be satisfied with his handiwork, and retires into the
tube to wait patiently for casual visitors.
July is a good month in which to experiment with _Agelena_, for if the
captives include female specimens some further spinning operations of
a very complicated description may be observed. The time of egg-laying
is at hand and elaborate preparations have to be made, but if the
experimenter wishes to see the whole process he must be prepared
to sacrifice his night’s rest, for the most critical part of the
performance takes place in the small hours of the morning. We will
describe what occurred in the case of one _Agelena_.
The approaching oviposition was heralded several hours beforehand by
the animal commencing to weave a hammock-like compartment from the roof
of the box and above the sheet-web. This chamber was about four inches
long and was constructed precisely in the same manner as the sheet, to
which it was braced by lines from various points of its under surface.
Its construction occupied the whole day previous to the laying of the
eggs, and not until half an hour before midnight was it completed.
Within this compartment, close to the roof, the spider next wove a
small sheet one inch long, working diligently in an inverted position,
ventral surface upwards. After a quarter of an hour it rested for an
equal space, apparently exhausted by its prolonged efforts. An hour
and three quarters intermittent work served to complete the sheet,
the spider varying the monotony of its sinuous walk round this small
area by occasionally walking over it and strengthening the lines which
attached its angles to the roof.
[Illustration: Fig. 5. _Agelena_ weaving her egg-cocoon.]
A marked change now became observable in the manner of working. The
animal abandoned its incessant to and fro motion but began to jerk its
body up towards the sheet, throwing silk strongly against it. At the
same time the posterior spinnerets were actively rubbed together and
the long posterior spinnerets separated and brought together again
with a scissor-like action. The result of this performance was to
invest the under surface of the small sheet with a coating of flossy
silk quite unlike the ordinary web in texture, the purpose of which
soon became evident, for at about a quarter past two the spider began
to deposit its eggs _upwards_, against this loose-textured silk,
aiding the egg-mass to adhere by occasional upward jerks of the
body. This occupied between five and ten minutes, and as soon as it
was accomplished the under surface of the egg-mass was covered by a
layer of flossy silk similar to that against which it was laid, the
eggs being thus entirely enveloped in a coating of soft loose-textured
material. This was next covered in by a sheet of firm texture like that
of the original web.
It might be supposed that the work was at length finished and that
a well-earned rest might be enjoyed, but this was far from being
the case. The spider remained as active as ever though an hour or
two passed before the object of its industry was evident. All this
time it was incessantly climbing backwards and forwards between the
egg-sheet and the hammock and generally scrimmaging round in the most
unaccountable way, but it gradually became evident that the eggs were
being enclosed in a wonderful transparent box of filmy silk with the
egg-bearing sheet for its roof. By nine o’clock it was of moderate
strength and opacity, and the spider, having worked “the clock round,”
no longer laboured continuously. Days elapsed, however, before it was
entirely finished to the satisfaction of the spider, which remained all
the time in close proximity to the box and could with difficulty be
frightened away, but clung tenaciously to it when interfered with.
Now this remarkable performance, which any reader endowed with
sufficient patience may observe for himself, gives food for thought.
The spider has never seen a cocoon constructed and has no model to
work by, and yet it performs with absolute precision all the stages,
in their proper succession, of a work which involves quite a number of
different spinning operations, nor does the absence of light by which
to work trouble it in the slightest. It seems hard to believe that this
is not a sign of high intelligence and that the spider is probably
quite unconscious of the object for which it has laboured so long and
so aptly. But how otherwise explain this curious fact? If the eggs are
removed the moment they are laid the work is continued precisely as if
they were still there. The box is laboriously built round the place
where they ought to be, and the spider refuses to budge from the empty
casket, though there is no longer any treasure to guard.
Clearly as the egg-laying time approaches the spider feels an
irresistible blind impulse to perform in a definite order certain
complicated actions. It is like a machine actuated by an internal
spring, and in the spider’s case the internal spring is the inherited
nervous mechanism we call instinct, which urges it to actions which it
is not in the least necessary that it should understand.
CHAPTER VII
WATER-SPIDERS
Here is the place to insert a short account of some near relations of
_Agelena_ which we shall certainly not meet in our walk, but of which
the mode of life is too interesting to be altogether passed over in
silence.
We have seen that the class Crustacea (crabs, shrimps, etc.) is the
great division of the Arthropoda entirely adapted to an aquatic life,
breathing, by means of gills, the air which is dissolved in the water.
Insects and spiders are air-breathing, and properly belong to the land;
yet there are many insects which pass their early stages—often the
greater portion of their life—in the water, and some which are very
fairly at home there when adult. Such insects often have gills when
young, and are therefore at that period true water animals, like the
Crustacea.
The Arachnida—that division of the Arthropoda to which the spiders
belong—include a few groups which permanently inhabit the sea, and
could not live on land. There are even some weird creatures called
Sea-spiders (Pycnogonids), but these do not concern us, for they are
very far removed from the true spiders which are the subject of our
investigations.
Now the true spiders are always air-breathing, and if they venture
into the water at all they must frequently come up to the surface
to breathe, or else they must store up a reservoir of air beneath
the surface of the water if they are to avoid death by drowning.
Nevertheless some of them have been hardy enough to encroach on the
domain of the Crustacea. Not a few are able to run freely on the
surface of the water and even to dive occasionally for the purpose
of seizing one of its denizens, but the number of those which have
succeeded in really adapting themselves to aquatic life is very
limited, and is, as far as we know, restricted to two small groups,
both of them members of the Agelenidae.
Among the coral reefs of the Indian and Pacific oceans, and also off
the southern coast of Africa there are found spiders of the genus
_Desis_ which spend almost all their time under the surface of the sea,
from which they only emerge at low tide. They construct very closely
woven tents, impermeable to sea-water, which imprison air at low tide,
generally choosing for the purpose some cavity which has been excavated
by one of the burrowing molluscs. Beyond this we really know very
little about them, and there is much difference of opinion as to the
mode in which they obtain their food. Some writers state that they only
leave their shelters at low tide to chase small crustaceans, and that
when placed in vessels containing sea water they are quite helpless
and soon drown. On the other hand one observer found that a species of
_Desis_ was quite at home in a sea-water tank, in which it swam freely
and even attacked and fed upon a small fish. Possibly different species
of the genus behave in different ways, some being more truly aquatic
than others, though it is certain that the troubled waters of a coral
sea are not a very promising field for sub-aqueous operations. We know
a great deal more of the mode of life of those Agelenids which have
taken to living in fresh water. Indeed the subject of the water-spider,
_Argyroneta aquatica_, is so hackneyed that in dealing with it we shall
probably be telling the reader much of what he knows already, but that
possibility must be risked.
There is, then, in many of our lakes, ponds and slow-flowing rivers
with a weedy bed, a spider which has entirely taken to a water life,
and for which it is useless to search on land. It is a docile captive,
and consequently a favourite subject for transference to an aquarium,
where its habits can be observed at leisure. Its first care is to
construct beneath the water a small dome-shaped web, open below, and it
generally selects the under surface of the leaf of a water weed for the
purpose of anchorage, though a ready-made shelter is often furnished by
the empty shell of some fresh-water mollusc. Its next proceeding is to
fill this retreat with air in a very ingenious manner.
While swimming about in the water the spider has a most striking
appearance, its abdomen almost resembling a globe of quicksilver.
This is because the body is enveloped in a bubble of air, retained
largely by the long hairs with which it is clothed. Thus it carries its
atmosphere about with it, and as often as not it swims with its back
downwards, which has the effect of bringing the bulk of the air-bubble
towards its ventral surface, where the breathing pores are situated.
Now when the dome-shaped web is ready to be filled with air the spider
rises to the surface, lifts its abdomen above it, and brings it down
with a flop, thus imprisoning an extra large air-bubble which it
embraces with its hind-legs by way of holding it more securely, and
then, swimming rapidly down by means of its other legs to the web it
discharges its load of air beneath the downwardly directed mouth of the
dome.
By a frequent repetition of this process the dome is at length filled
and converted into a veritable diving-bell, in which the spider can
exist quite comfortably until the supply of oxygen in the imprisoned
air is exhausted and has to be renewed. From this base it issues forth
to feed upon fresh-water insects and crustaceans, sometimes even
attacking small fishes.
The proceedings of the male _Argyroneta_ in the mating season are
very curious. He seeks out the tent of a female and sets up his own
establishment—generally somewhat smaller—close at hand, filling it
with air in the approved manner. He then builds a sort of corridor
uniting the two domes, and when this is complete he bites through
the female dome, thus uniting the two air reservoirs by means of a
connecting tube. Not seldom it happens that the female is in no mood
for dalliance, and a battle royal ensues, with disastrous results to
both domiciles and the tube that connects them. The male, however,
is in this case well able to hold his own, for he is larger than
the female, a phenomenon elsewhere unknown in the spider realm.
_Argyroneta_ lives for some years, and makes two diving-bells each
year—one near the surface in summer and one at a greater depth in
winter. It was thought at first that one was constructed especially for
receiving the eggs and the other as a habitation, but the egg-cocoon
may be found in either, for there are two broods in the course of the
year. The winter dome is of very dense silk, glossy in appearance, and
giving the effect of a uniform sheet of silky material rather than a
fabric. Moreover its mouth is closed, and the spider remains inactive
within. It is this winter domicile that is most frequently found in the
shells of molluscs. The egg-cocoon is also dome-shaped, having a convex
upper and a flat under surface. The newly hatched young inhabit their
mother’s tent for a time and then set forth in the water to seek their
living and set up establishments on their own account.
There is only one known species of _Argyroneta_, widely distributed
in the temperate regions of Europe and Asia. The female is about
half-an-inch long, of no particular beauty out of the water, its colour
being reddish-brown, and its body and legs very hairy. There are,
however, a few New Zealand spiders rather closely allied to it and of
very similar habits.
CHAPTER VIII
CRAB-SPIDERS. MIMICRY
All spiders can spin, but by no means all use that power to entrap
their prey. Many have no settled abode or resting place except perhaps
for a short time when they are rearing their young. Among these roving
tribes, there are three groups which may engage our attention for a
time—the Crab-spiders (Thomisidae), the Wolf-spiders (Lycosidae) and
the Jumping spiders (Attidae).
Crab-spiders are seldom seen by the ordinary observer, for their
habits do not bring them prominently into notice, and many of them
are of small size. They are well named, for there is something
exceedingly crab-like in their appearance and in their actions. Their
body is generally broad and flattened, and their legs, instead of
being arranged fore and aft, like those of most spiders, extend more
or less laterally, and though they can move pretty actively in any
direction their normal method of progression is sideways. Then again,
when frightened they cramp their legs up under their bodies in a most
crab-like fashion and “sham dead.”
[Illustration: Fig. 6. A Crab-spider (_Thomisidae_), × 3.]
We saw some of these spiders on the iron railing, but their real haunts
are among grass and herbage or upon the trunks of trees. Some are true
rovers, hunting their prey by day and camping out wherever they happen
to find themselves at night. Their methods are without guile—except
that they approach their victims warily; their trust is in rapidity
of action and superior strength. But other crab-spiders lead a less
strenuous life; their habit is to lurk in moss, lichen, or flowers till
an insect draws near enough to be seized without any great expenditure
of energy.
Now in the case of some of these spiders the chance of obtaining
a meal is very greatly increased by a remarkable similarity of
coloration between the spider and its usual hunting ground. The
spider’s object is to remain invisible, and concealment is obviously
more easy if its colour matches that of its environment. To a greater
or less extent this protective coloration as it is called prevails
universally:—spiders are seldom conspicuous objects among their usual
surroundings, but it is only occasionally that we meet with cases of
very remarkable colour adaptation. Two such, however, occur among
English crab-spiders. One is a species not uncommon in the south of
England, and fairly plentiful in the New Forest, where it is to be
sought among the lichen on the tree trunks, where its blue-grey body,
marked with black and white blotches makes it practically invisible
except when in motion. It rejoices in the name of _Philodromus
margaritatus_. The other case is that of the spider known as _Misumena
vatia_, which is variable in colour, some specimens being yellow and
others pink, while a variety of the species has a blood-red streak
decorating the front part of its abdomen. If it were to choose lichen
as a hunting ground there would be little chance of concealment, but
it does nothing so foolish:—it hides among the petals of flowers,
generally, but not always, among flowers more or less of its own colour.
Now this phenomenon of resemblance is sometimes carried very much
farther than a tolerable correspondence between the colour of an
animal and its surroundings; it occasionally amounts to an apparent
imitation, in form and in behaviour as well as in colour, of some
other object, either animal or vegetable and in such cases we have
examples of what is known as Mimicry. Most people have seen remarkable
instances of this phenomenon in the “stick” and “leaf” insects of
entomological collections. There are several different ways in which
such a resemblance may be profitable to the imitator. Clearly it may
be advantageous for a weak animal to be mistaken for one much more
formidable and less likely to be attacked, or for an insect which is
really extremely good eating to resemble closely one which birds well
know to be unpalatable. Or again, if your line is to lie _perdu_ and
wait for some unwary insect to come within reach, it must be a distinct
asset to be indistinguishable from such an innocent object as a twig
or a leaf; and the same disguise may serve you if you are the possible
victim and you can make the would-be devourer believe that you are a
mere vegetable.
It is seldom difficult to see some such possibility of gain in the
numerous well-known cases of insect mimicry. The wasp tribe—formidable
with their stings—are often “mimicked”; the unpalatable Heliconid
butterflies are “imitated” by members of edible families, and some
insects are such exact imitations of leaves that the all-devouring army
ants have been seen to run over them without discovering the imposition.
“Mimicry” is an unfortunate term inasmuch as it seems to imply
intentional imitation; “protective resemblance” is better. It is
generally accounted for by the action of “natural selection” upon
random variations. No two members of a brood are exactly alike; slight
variations in form, size, colour, etc., are constantly occurring, and
when the variation is a useful one the animal possessing it has a
slightly better chance of surviving and rearing progeny, some of whom
will probably possess the same peculiarity, perhaps even in a more
marked degree, and will be better equipped than their neighbours in the
struggle for life. The happy possessors of such favourable variations
are thus in a sense “selected” by nature, and this selection, acting
through countless generations, is thought to be the chief agent in
bringing about the remarkable phenomenon of protective resemblance.
The theory has, no doubt, been pushed too far; fanciful resemblances
have been detected and advantages of which there is no proof are
sometimes asserted, and moreover other possible ways of accounting for
the facts have been too much overlooked.
But however it has come about, there is a case of “mimicry” among
crab-spiders which deserves more than a passing mention. The name
of the spider in question is _Phrynarachne decipiens_, and it was
accidentally discovered by Forbes when butterfly-hunting in Java. It
spins a white patch of silk on the upper side of a leaf on which it
places itself back-downwards, clinging to the web by means of spines on
its legs. It then folds its legs closely and lies absolutely still. In
this position the spider and web look precisely like the dropping of
some bird upon the leaf; such droppings are frequently seen, and seem
to be particularly attractive to butterflies. It was not until Forbes
tried to catch a butterfly settled on a leaf that he found that what
looked like excrement was really a spider which held the butterfly in
its grasp. Even after this experience he was again deceived by the same
species in Sumatra.
There are several extremely ant-like spiders, and it is remarkable that
some of the imitators belong to widely different spider families:—that
is to say the resemblance has arisen independently from quite different
starting points.
It is very noteworthy that resemblance in structure is always
accompanied by similarity of behaviour—as indeed it is bound to be
if any benefit is to accrue to the mimic. Your resemblance to a leaf
will deceive no one if you run wildly about, and your imitation of an
ant will lack verisimilitude if you adopt a slow and stately method
of progression. Ant-like spiders adopt the hurried and apparently
undecided gait of their models, and insects which look like sticks,
leaves, or inanimate objects all possess the power—and the habit—of
remaining for a long time perfectly motionless.
CHAPTER IX
WOLF-SPIDERS
Of the groups of wandering spiders, which spin no snare but trust to
speed and agility for their food, the Lycosidae or wolf-spiders supply
the best subjects for study. To begin with, they are very numerous
at certain times of the year, some species absolutely swarming in
woods during May and June among the leaves which fell in the previous
autumn. During the summer months they are still in evidence, but
as winter approaches they rapidly disappear. The swift motion and
predaceous habits have earned them the name of wolf-spiders, but
though they sometimes occur in incredible numbers so that it seems
impossible to avoid treading upon them, they do not hunt in packs; each
one is entirely concerned with his own individual quarry. They are
moderate-sized or large spiders—commonly about half an inch long in
this country though there are exotic species which attain an inch and
a quarter—and in build they are very unlike the garden-spider, being
elongate, and with the abdomen nothing like so globular.
Their habits vary considerably. One genus, appropriately named
_Pirata_, is semi-aquatic, living at the margins of rivers and ponds,
and able to run on the surface of the water, but most of the Lycosidae
prefer dry land—the dryer the better. Heaths, sandhills, bare and
stony stretches of soil, even deserts, are fertile in examples of this
group. Most of the smaller species love the sunlight, and it is often
noticeable on a bright day, when the ground seems to be alive with
wolf-spiders, that a chance cloud obscuring the sun will cause them to
disappear as if by magic.
Some of the small Lycosids seem to be absolute wanderers, having
no home at all, but spending the night under a stone or any casual
shelter, while others dig a more or less temporary hole in the ground
into which they carry their captured prey, and in which they take
refuge on the appearance of an enemy. The large wolf-spiders have
permanent burrows from which they do not wander far and in the mouths
of which they spend most of their time, on the look out for passing
insects.
Let us first catch one of the small wolf-spiders and examine it.
This is not a very simple operation with creatures which can run so
swiftly, but after a few attempts we induce a specimen to run up
into a glass tube held in the line of its course. We see it to be a
long-bodied spider thickly beset with hairs which entirely hide the
integument of the abdomen. Its general hue will probably be a dark
grey, and its abdomen will be decorated by a more or less distinct
pattern due, not as in the garden spider to pigments in the skin, but
to the coloration of the hairs. But look particularly at its eyes. A
pocket-lens will suffice to reveal that two of them are much larger
and much more business-like in appearance than anything _Epeira_
had to show. These are directed forwards, being placed at the upper
angles of the perpendicular front face, so to speak, of the animal.
Below them, just above the jaws, are four small eyes in a transverse
row, and behind them at some distance, on the upper surface of the
cephalothorax, are yet another pair of moderate size. In some groups
of spiders the eyes are not only small but have an indefinite, dull,
ineffectual appearance; here they are clear-cut, glossy and convex;
sight apparently counts for something in the case of the Lycosidae.
And this is what we should expect. A sedentary spider is informed
of the whereabouts of its prey by the sense of touch, through the
trembling of the web, but a wolf-spider spins no web and is dependent
on the keenness of its vision.
There is a very prettily marked English Lycosid which is often found on
sandhills, in situations particularly convenient for observation. Its
name is _Lycosa picta_, and it is incidentally interesting as affording
a good example of protective coloration, for the sandhill variety is
light-coloured and very inconspicuous when stationary on the sand,
while an inland variety not uncommon on the dark soil of heaths is of
a much darker hue. Carefully scrutinising the firmer sand of the dunes
on a sunny June day, I detect a number of small holes—the burrows of a
colony of these spiders—and approaching cautiously I establish myself
at full length at a distance of a yard or so on the side away from the
sun, in such an attitude that I can observe closely for a considerable
time without too much discomfort. The minutes pass and nothing
happens, but I know that the cardinal virtue of the naturalist is
patience, and I wait. Presently the dark circle of one of the burrows
is obliterated—it is filled by the sand-coloured head of the spider,
coming up to prospect. Other heads appear, and soon one spider, bolder
than the rest, emerges bodily, and remains for a minute motionless, on
the _qui vive_. Finding no cause for alarm, it presently begins moving
about stealthily, and before long several members of the colony are
busily exploring the neighbourhood. A cloud passes over the sun and all
quickly disappear into their holes, but this time without alarm, for
they come forth unhesitatingly when the sun shines again.
It is a fascinating sight to observe these little creatures pursuing
their operations in absolute silence under my very eyes. A few stealthy
steps are taken, the body being so moved that the battery of eyes is
brought to bear upon different points of the compass; a short quick run
ensues, followed by more cautious movements. I am not fortunate enough
to see the actual running down of a quarry, but in time I note one of
the colony bringing home an insect in its jaws. So absorbed am I that I
fairly jump when a horrified human voice close at hand observes “He’s
in a fit”! I have excited the solicitude of a girls’ school which has
approached noiselessly over the sand on their afternoon promenade, and
stands gazing at me with as much fascination as I at the spiders. I
hasten to reassure them, but the spell is broken, and the séance is at
an end. Not a spider is visible.
But I can still do one thing. Here is a good opportunity of finding
out something about the burrows of these spiders. In turf the
investigation would be difficult, but it is easy to operate in the
tolerably firm sand where the colony has established itself.
I insert a straw into one of the burrows as a guide to the exploration,
and with a knife carefully begin to remove the sand immediately round
it. It is lined, I find, by a very delicate and slight coating of silk,
no more than sufficient to keep the sand particles of its walls from
falling down into the tube. I go down for an inch and a half or so and
find that the tube ends blindly in a sort of silk-lined pocket, but
no spider is there! This is mysterious, for I am pretty sure that my
spiders are at home.
I go to work upon another burrow, but this time in a different way,
digging it out bodily with its surrounding sand, and placing it on
a sheet of paper, with which I am luckily provided, for a detailed
examination. I can now approach it from the side, and by carefully
removing the sand, lay bare the whole silken tube. As before there is a
straight perpendicular burrow, ending blindly, and uninhabited, but at
a point at about half-way down the tube I find a branch bending upward,
so that the whole tunnel is +Y+ shaped, and at the blind end of
this branch I find the spider.
This observation suggests that the tunnels of some of our English
wolf-spiders may be more complex than was imagined. At present nothing
is known of their nature in the case of other species.
A little later in the summer the appearance of a troop of wolf-spiders
has undergone a marked change; almost every individual will be found
burdened with a circular bag of eggs attached firmly to its spinnerets,
and carried about with it in all its wanderings.
[Illustration: Fig. 7. Wolf-spiders; _A_, with egg-cocoons; _B_, with
young on its back.]
The “cocoon” is worth examination. It is a rather flattened sphere,
with an equatorial line round it, giving the effect of two halves—an
upper and a lower. The operation of making it has very seldom been
observed, because it takes place in a closed retreat constructed for
the purpose. McCook was fortunate enough to see something of it in the
case of a captive _Lycosa_ which he kept in a glass jar partly filled
with soil. Luckily the spider dug its tunnel for cocooning purposes up
against the side of the jar, so that its interior was visible. It was
about an inch deep and fairly wide, and its aperture was closed with
silk.
Against the perpendicular wall of soil a circular silken cushion about
three quarters of an inch in diameter was spun, and the eggs deposited
in the centre. The edges of the cushion were then gathered up and
pulled over the eggs, and the bag thus formed was finished off with an
external layer of spinning work on the two halves of the sphere, the
seam or “equator” being left thin for the exit of the young spiders.
The _Lycosa_ then attached the cocoon to its spinnerets and proceeded
to bite away the silken sheet which sealed the burrow. The whole
operation lasted about four and a half hours.
Thenceforward, till the young are hatched, the wolf-spider never quits
her egg-bag, which she carries about on all her expeditions attached by
threads to the spinnerets. Garden-spiders die soon after laying their
eggs and never see their progeny, but here we have a case of maternal
solicitude persisting for many days, and the Peckhams seized upon it as
a good subject for investigating the subject of the memory of spiders.
If the cocoon were removed from the spinnerets, after how long an
interval would it be recognised by the mother?
A _Pirata_ was selected for experiment. It offered great resistance
to the removal of the cocoon, seizing it with its jaws and trying to
escape with it. When it had been taken away the mother displayed great
uneasiness, searching for it in all directions. It was returned to her
after an hour and a half, when she received it eagerly and immediately
attached it in the usual position.
From three others of the same species the cocoons were removed and
restored after thirteen, fourteen and a half, and sixteen hours
respectively. All remembered them and took them back immediately. But
twenty-four hours seemed to be the extreme limit of their memory;
after that interval two of the mothers refused to have anything to
do with their cocoons, while the third only resumed hers, slowly and
without any enthusiasm, after it had been placed before her seven
times in succession. Some other species seemed to possess a rather
longer memory, but the experimenters found no Lycosid constant in her
affection for so long a period as forty-eight hours.
We have said that Lycosid spiders see comparatively well; yet, if
they are placed within an inch or two of their cocoons they may be
quite a long time finding them. This is very puzzling until it is
considered that its habitual position is such that the spider never
sees it. She never has seen it since its construction, and does not
in the least recognise it by sight. Spiders of other groups, where
the female remains near but detached from the cocoon, are not at the
same disadvantage, and if the cocoon is removed to a short distance
the mother will go straight to it and bring it back. The wolf-spider
only knows the _feel_ of the cocoon; she may pass close by it without
recognition, but as soon as she touches it the cocoon is immediately
resumed—if the interval of separation has not been too great.
But is it necessary to restore to the spider her own cocoon? Will not
that of another spider serve as well? Certainly it will; a wolf-spider
will eagerly adopt the cocoon of a spider even belonging to a different
genus, if not greatly unlike her own in size. Nay, even a ball of pith
of the same size will be attached with alacrity to the spinnerets,
though if offered a choice between a cocoon and a pith ball the
spider, after some hesitation, selects the real article. One spider
even accepted a cocoon into which a leaden shot had been inserted,
making it many times its original weight. She could hardly crawl with
her new burden, but stuck to it gallantly, and when several efforts
to secure it to her spinnerets had proved ineffectual she carried
it about between her jaws and the third pair of legs. Again we find
the intelligence of the spider distinctly limited, but its powerful
instincts are equal to all ordinary requirements. Nature does not,
as a rule, play extravagant pranks, such as interchanging cocoons or
substituting for them pith balls and leaden pellets.
The famous Tarantula is a wolf-spider, though in America,
unfortunately, the name has been quite wrongly applied to the members
of an entirely different group. Everyone has heard of its deadly
repute, and of the myth that its bite can only be cured by the wild
tarantula dance or tarantella. It is one of the large Lycosids of
southern Europe. These, as we have said, are much less nomadic than
the smaller species, but have a permanent home, from which they do not
wander far afield. They prefer waste, arid places, and their burrows
are simple cylindrical tubes with the upper portion lined by silk, the
mouth being often surmounted by a sort of rampart of particles of soil
mingled with small pieces of wood collected in the neighbourhood. The
spider lurks in the mouth of the tube where its glistening eyes can be
distinctly seen. If an insect ventures near it rushes out and secures
it; if alarmed, it retreats instantly to the bottom of the burrow.
That most fascinating of all entomological writers, J. H. Fabre, made
some observations on a tarantula of southern France which well deserve
attention. Colonies of the spider were numerous in his neighbourhood,
and he set himself to procure some specimens. Old writers assert that
if a straw be inserted into the burrow the spider will seize it and
hold it so firmly that it may be drawn forth. Fabre found this method
exciting, but uncertain in its results. Another plan which had been
advocated was to approach warily and cut off the retreat of a spider by
plunging the blade of a knife into the soil below it and so cutting off
its retreat, but this required very rapid action, and was, moreover,
apt to be prevented by the presence of stones in the soil. He devised
a new scheme. He provided himself with a number of “bumble” bees in
narrow glass tubes—about the width of the spider burrows. Repairing
to a tarantula colony he would present the open end of the tube to
the mouth of a burrow. The liberated bee, seeing a hole in the ground
exactly suitable for its own purposes, would enter it with very little
hesitation. There would be a loud buzz and then instant silence.
Inserting a pair of forceps into the hole, Fabre would then withdraw
the bee with the spider clinging tenaciously to it. In all cases the
death of the bee was instantaneous, though the closest examination of
its dead body revealed no wound.
Now Fabre was fresh from his wonderful studies of the habits of the
solitary wasps, which provide their young with insects stung in such
a way as to cause paralysis but not death. In their case the problem
was to secure food for their larvae which should remain fresh for
many days, an instinct taught them to solve it in the most remarkable
manner. The problem of the spider was different. It was a case of
killing instantly, or being killed; a merely wounded bee is as
formidable as one unharmed. What Fabre desired to know was this: did
the spider trust to one invariable deadly stroke in dealing with the
bee, as the solitary wasp, according to its species, had been found to
act always precisely in the same way in paralysing its victim?
To settle this point the spider must be seen at work, and the obvious
plan seemed to be to enclose a bee and a tarantula in a glass
vessel and see what would happen. But nothing happened at all. The
spider, away from its burrow, refused to attack. The equally matched
antagonists treated each other with the greatest respect and only
evinced a desire to keep as far apart as possible. Even when placed in
the same tube both acted on the defensive, and no light was thrown on
the problem.
But Fabre’s ingenuity was equal to the occasion. It occurred to
him that to use as a bait an insect of burrowing habits had been a
tactical error; if instead of a bumble bee some other insect, equally
formidable, but not attracted by holes in the ground, were selected for
the purpose, the spider might be induced to rush forth and reveal its
method of attack.
A large carpenter bee—_Xylocopa_—was chosen and the mouth of
the tube containing it was presented as before to the mouth of the
tarantula tunnel. The insect showed no disposition to enter the tunnel,
but buzzed in the tube outside. Many burrows were tested before any
luck attended the investigator, but at length a spider responded.
There was a fierce rush, a clinch, and the bee was dead; the operation
was too rapid to follow, but the spider’s fangs remained where they
had struck—embedded just behind the insect’s neck. The experiment
was repeated until sufficient cases had been witnessed to establish
the fact that the tarantula dealt no random stroke but with unerring
precision and lightning rapidity plunged its fangs into the vital spot.
Fabre quaintly exclaims “J’étais ravi de ce savoir assassin; j’étais
dédommagé de mon épiderme rôti au soleil!”
Examples of the same species of tarantula kept in captivity threw
further light of the habits of the group. These large Lycosids live for
years, and though stay-at-homes when _rangé_ so-to-speak, they are at
first wanderers on the face of the earth. They do not settle down and
burrow till the autumn just after they have attained maturity. These
young adults are only about half the size they will eventually attain,
but the burrows are enlarged at need, so that it is customary to find
tubes of two sizes—those of the newly established small females, and
those of the fully-grown females of two or more years old.
Curiously enough, if disturbed, they entirely decline to burrow
unless it be the proper season for that operation, but remain inert
and helpless on the surface till they die. If, however, a tunnel is
provided for them, they enter it at once and adapt it to their needs.
The legs take no part in the burrowing process, which is entirely
carried out by the jaws. With infinite labour small particles of
earth are dislodged and carried by the mandibles to be dropped at a
considerable distance from the nest.
The parapet round the mouth of the tube is in nature usually quite
a small erection, but this seems to be due to the fact that only
a small amount of suitable material is available in the immediate
neighbourhood, and the spiders will not go far afield. In captivity,
when abundance of material was supplied, they attained a height of two
inches. Small stones, sticks, and strands of wool cut into lengths of
one inch and of various colours were placed within reach, and all were
used in building the parapet. Comparatively huge pebbles were rolled up
for a foundation, and fragments of earth and pieces of wool entirely
irrespective of colour were bound together by irregular spinning work.
On sunny days the spiders would crouch behind the parapet with their
eyes above its level. To distant insects they paid no attention, but
if one approached within leaping distance, it was pounced upon with
unfailing accuracy.
In due season the captives laid their eggs and enclosed them in the
regulation cocoon which they attached to their spinnerets, never
parting from them thenceforward, though considerably hampered by them
in their movements up and down the tube. But a very remarkable change
now took place in their behaviour at the mouth of the tunnel. In sunny
weather, instead of remaining, as Fabre puts it, “_accoudé_” on the
parapet, they reversed their position, raised their egg-cocoons with
their hind legs, and slowly and deliberately turned them about, so that
every part in succession should be exposed to the sun’s rays.
We now come to a remarkable habit possessed by all the Lycosidae.
When the young are ready to leave the cocoon they find an exit at
the thinner equatorial seam, and proceed immediately to climb on to
the back of the mother, clinging firmly to her covering of hairs.
If a wanderer, she carries them thus on all her expeditions; if a
stay-at-home, they accompany her up and down her tube. They are often
dislodged—indeed, when alarmed, they scatter for the moment, but when
the peril has passed they immediately swarm up the maternal legs to
their former position.
Now in the case of the tarantula, it is seven months before they are
able to fend for themselves. Meanwhile they eat nothing, and look on
with indifference while their mother feeds. She not only carries them
willingly, but exhibits solicitude when deprived of them, but she shows
no discrimination as to her own offspring, and is quite content with
those of another spider. The young, when brushed off, climb the legs
of the nearest female, and a spider may thus be laden with thrice her
proper load without any protest. They form a layer two or three deep,
and can then only find room by covering the whole of her back. They
nevertheless take care not to obscure her vision by covering her eyes.
Two mother tarantulas, each with her young on her back, came into
contact, and a battle _à outrance_ took place. One was slain, but the
double brood, scattered by the conflict, on its cessation climbed on
to the back of the victor, and remained calmly in position while she
proceeded to dine in leisurely fashion on the vanquished!
In March, seven months after hatching, the young were ready to
start life for themselves. Their first action was to climb to the
highest points attainable, whence they set sail in the manner already
described, and were borne gently away in the air.
We can hardly leave the tarantula without saying something on the
vexed question of spider venom. All over the world there are certain
particular spiders whose bite is especially feared. Among them are
the “Tarantula” and the “Malmignate” of southern Europe, the “Vancoho”
of Madagascar, the “Katipo” of New Zealand, and the “Queue rouge”
of the West Indies. Quite an extensive literature has arisen around
the subject but its perusal leaves one not much wiser than one was
before. Circumstantial accounts of deaths from the bite of a spider
are countered by the assertions of experimenters that they have
allowed themselves to be bitten repeatedly by the same species without
suffering any inconvenience. There is at all events some basis for
the popular view in the fact that all spiders possess a poison gland
which is analogous to that of the snake inasmuch as it opens near the
tip of the fang which is plunged into the animal attacked. In the case
of the large, powerful spiders of the family Mygalidae, and perhaps
in the tarantulas the effects of the bite on higher animals are not
negligible, and clearly exceed the results of a mere puncture. A young
sparrow and a mole bitten by Fabre’s tarantula in spots by no means
vital died within a few hours. But it is a very remarkable fact that
many of the most dreaded spiders are neither large nor powerful. The
“Malmignate,” the “Vancoho,” the “Katipo,” and the “Queue rouge” are
all members of the comparatively weak-jawed Theridiidae, and their only
striking characteristic is vivid coloration, all being marked with
red spots. It is probable that their deadly powers are almost entirely
fabulous; and that they have been singled out as particularly dangerous
merely because of their conspicuous appearance.
The smaller species are certainly harmless as far as man is concerned,
and it is even disputed whether their poison plays much part in
the ordinary slaying of insects. The very inconsistent results of
experiments may be due to some control exercised by the spider over the
output of poison. There is no proof that its ejection is automatic,
and it is quite possible that the spider is economical in its use. Or
again, in some of the cases of innocuous biting, the supply of venom
may have run short.
CHAPTER X
JUMPING SPIDERS
We are not in the land of the jumping spiders or Attidae, and our few
and sober-coloured examples of the group give but a feeble idea of the
Attid fauna of tropical countries where these creatures abound and
often rival the “ruby-tail” flies in the brilliancy of their hues.
[Illustration: Fig. 8. Salticus scenicus, female, × 4.]
It is one of the largest groups, numbering several thousand species,
but the British list includes barely thirty, and most of these are
of rare occurrence, or at all events exceedingly unlikely to be met
with by any but the most energetic collector. Indeed it may be said
that there is only one British species which we may look forward with
tolerable confidence to finding upon some sunny wall or fence in the
summer, in whatever part of the country we may be. This is _Salticus
scenicus_, sometimes called the Zebra Spider. Though absolutely
dowdy in comparison with most of its tropical cousins, it is a not
unattractive little creature, and illustrates sufficiently well the
characteristics of its tribe. Armed with a pocket-lens, a glass tube
or two, and—more necessary still—the very largest amount of patience
we can summon, we go in quest of the zebra spider. A tarred fence is
a good hunting ground, because the spider, if present, is readily
seen, but if this is drawn blank we must have recourse to a wall, where
sharper eyesight will be required.
[Illustration: Fig. 9. “Face” of an Attid spider, shewing the anterior
eyes and the chelicerae.]
Our quarry is of small size, not more than a quarter of an inch long
in the body, which resembles that of the wolf-spiders in build, the
abdomen not rising above the level of the fore-body or cephalothorax.
It is thickly clothed with short hairs—black, white, and grey—so
arranged as to show oblique zebra-like stripes on either side of the
abdomen. The legs are short and robust, very different from the long
thin limbs of the garden-spider; especially strong are the fore-legs.
The head is broad and square, with a high perpendicular forehead, but
the most remarkable features are the eyes.
On the vertical front are four splendid eyes. The wolf-spider’s eyes
were large, but these, in comparison, are immense, especially the
median pair. Their axes are directed straight in front. Four other eyes
are placed on the top of the head, far apart from each other, the
more forward pair very small, the hind pair of moderate size. In some
Attid spiders these great anterior eyes are wonderful objects under
the microscope, deep sea-green in hue and fringed with coloured hairs.
They form a veritable battery which the spider brings to bear upon the
object of its chase. Human eyes, to match them in comparative size,
would literally have to be as large as saucers!
If we are in luck, we soon descry a _Salticus_ showing up boldly
against the black surface of the fence, and to set ourselves to watch
its antics attentively. One thing strikes us at once; it is quite at
home on a perpendicular surface—nay, on the under side of a horizontal
beam, for that matter. Now a garden-spider would have great difficulty
in maintaining itself in such a position unless well supplied with
silken lines to which to cling; evidently there is some difference
in the structure of the feet of these spiders which may be worth
investigating later on.
Also we notice some odd tricks of movement in the jumping spider;
a curious way of exploring the surface on which it is working by a
succession of short runs alternately with periods of absolute stillness
as though on the _qui vive_; a noticeable freedom of movement between
the fore- and the hind-bodies so that its battery of eyes may be
directed to this side or that; sometimes an elevation of fore part as
though for the purpose of obtaining a wider view.
We may have to wait long before we see it successful in the chase. It
will often patiently explore a large area, testing the surface with
its palps as it goes, without any obvious reward. It conscientiously
searches all depressions and crannies, and, sometimes remains in them
for a considerable time—perhaps to devour some minute creature which
did not call into play its special methods of attack. At last it sights
a small insect which has alighted on the fence a few inches away; we
see it turn its head in that direction and remain motionless. Soon it
begins to edge nearer in a stealthy manner, striving to approach its
prey from behind, till, with a sudden spring, it pounces on its back.
Not always is the spring successful; often the insect sees its peril
at the last moment and takes to wing. But in this case, how does the
spider avoid a fall? We see, what we had not noticed before, that it is
anchored to the fence by a silken line; indeed all the time it has been
hunting it has been trailing behind it an exceedingly fine thread of
silk which it has attached at frequent intervals to the fence, so that
it can check its fall at will in the case of accident. At the right
angle, we may see the delicate filaments glistening in the sun over the
surface of its explorations. The garden-spider entangles its prey in a
web, the wolf-spider runs it down by sheer strength and speed, but the
jumping spider stalks it like a Red Indian.
The actions of the spider make it quite evident that its power of sight
is well developed. Mr and Mrs Peckham, whose remarkable observations
on the mating habits of jumping spiders must presently be considered,
established friendly relations with some of their captives which became
so tame as to jump on their hands and take food from their fingers.
They frequently induced them to jump from a finger of one hand to one
of the other, gradually increasing the distance up to eight inches.
They also twice observed a male chasing a female upon a table covered
with jars, books and boxes. “The female would leap rapidly from one
object to another, or would dart over the edge of a book or a box so
as to be out of sight. In this position she would remain quiet for a
few moments and then, creeping to the edge, would peer over to see if
the male were still pursuing her. If he happened not to be hidden, she
would seem to see him, even when ten or twelve inches away, and would
quickly draw back.”
Moreover that they have the ability to discriminate colours has been
shown by their behaviour when imprisoned in cages consisting of a
series of communicating chambers each with a glass top of a different
hue. They show a marked preference for the red chamber under these
circumstances while the least attractive colour seems to be blue.
It has been known for a long time that the males of many kinds of
birds—and especially of the more ornamental species—are accustomed
to perform the most extraordinary antics in the presence of the female
at the time of mating. The Peckhams made the unexpected discovery that
precisely similar “love dances” took place in the case of the jumping
spiders. Even the comparatively sober-coloured “zebra spider” performs
a weird _pas seul_ in courting its mate, but its display is feeble
compared with that of some of the more ornate of the Attidae.
Certain isolated observations on captive jumping spiders led these
observers to suspect that the mating habits were unusual and worthy of
accurate investigation, and they laid their plans accordingly, taking
their summer holiday a month earlier than usual, so as to miss nothing
of the pairing season, and including in their party an artist whose
drawings should furnish an indubitable record of the attitudes assumed
by the male spiders in their evolutions.
On arriving at their destination they found a small species, _Saitis
pulex_, with no great claims to remarkable beauty, mature, and ready
to pair. A female was placed in one of the experimental boxes which
had been provided in advance, and a male was admitted on the following
day. He sighted her at a distance of twelve inches, and showing signs
of excitement, advanced to within about four inches and then performed
a most ludicrous dance—something in the nature of a “highland fling,”
in a semicircle before her, she, in the meantime, moving in such a
manner as to keep him always in view. His exact behaviour was this:
he extended all the legs—and the palp—on the left side, folding the
first two legs and the palp of the right side under him, and leaning
over sideways so far as nearly to lose his balance, and in this
attitude he sidled along towards the lowered (right) side till he had
described an arc of about two inches; then the position was instantly
reversed, the right legs being extended and the left folded under, and
the arc retraced. A male was seen to repeat this performance 111 times!
He then approached nearer and when almost within reach “whirled madly
around and around her, she joining and whirling with him,” after which
she accepted him as a mate.
The next species to engage attention was an _Icius_. It was noteworthy
that although the neighbourhood was well known to the experimenters
they had never met with this spider before, but for a few days it
swarmed on the fences just as birds are known to assemble from all
quarters for the so-called “love dances.” After the mating season the
spiders wandered off into the woods again and were seen no more.
[Illustration: Fig. 10. A male Attid spider (Astia vittata) dancing
before the female. (After Peckham.)]
The performance was much as before, but the spiders assumed different
attitudes. The female lay flat on the ground with her front legs
raised; the male danced on the six hind legs, with the front legs
lowered and meeting at the tips. The males of this species were
exceedingly quarrelsome, sparring frantically whenever they met, but
their battles were entirely bloodless. “Indeed,” say the observers,
“having watched hundreds of seemingly terrible battles between the
males of this and other species, the conclusion has been forced upon us
that they are all sham affairs, gotten up for the purpose of displaying
before the females, who commonly stand by, interested spectators.” In
the case of one species, after two weeks of hard fighting between the
males, the Peckhams were unable to discover one wounded warrior. The
females, on the other hand, were often really formidable. _Phidippus
morsitans_ is an example. The male has handsome front legs, thickly
fringed with white hairs, and he displays these to the best advantage
in his love antics. Two males supplied in succession to one female “had
offered her only the merest civilities when she leaped upon them and
killed them.”
In the case of most of the spiders whose love-dances were investigated,
the chief ornamentation of the male consisted of fringes of white or
coloured hairs on the face, the palps, and the front legs, and they
kept these parts always before the females, displaying their glories
to the utmost advantage. The male of _Habrocestum splendens_, however,
possesses an extremely brilliant abdomen, and, lest anything of its
beauty should be lost upon the object of his admiration, he varies the
ordinary performance in a remarkable manner. He often pauses in the
dance, and, raising his abdomen, “strikes an attitude” in which he
remains motionless for half a minute. Moreover he frequently turns his
back on the female—a most unusual occurrence in the course of these
antics.
The males of one species, _Philaeus militaris_, were observed to
capture and keep guard over young females, which they imprisoned in
webs spun for the purpose until they had undergone their last moult and
were mature, chasing away all intruders in the interval.
The jumping spiders furnish a much stronger case for those who believe
that ornamentation plays an important part in sexual selection
than do either birds or butterflies. With regard to the birds it
has been objected, first, that there is little evidence that the
females pay much attention to the antics of the males, and secondly,
that practically all the male birds pair, whatever their claims to
pre-eminent beauty. Now in the case of the jumping spiders the females
follow the performances of the males with the utmost attention, and
seeing that the males are present in large numbers when the females
begin to appear, the latter are certainly in the position to reject
such mates as do not please them.
The mere relation of the results of this most interesting investigation
conveys no hint of the unwearied patience and close observation
necessary to those who would surprise the secrets of nature. One is
apt to infer that it is only needful to place some spiders in a box,
establish oneself in an arm chair, and ring on the performance, so
to speak. The Peckhams modestly remark: “The courtship of spiders is
a very tedious affair. We shall condense our descriptions as much as
possible, but it must be noted that we often worked four or five hours
a day for a week in getting a fair idea of the habits of a single
species.”
CHAPTER XI
THERAPHOSID SPIDERS
It is quite impossible in a work like the present to deal with the
classification of spiders. About forty families have been established,
some of them of vast extent, the Attidae, for example, including some
four thousand species. The great French arachnologist, M. E. Simon,
has occupied 2,000 quarto pages in defining the families, sub-families
and genera, without concerning himself with the species at all! It is,
however, desirable, that the attention of the reader should be called
to the primary division of the group, according to which all spiders
are either _Araneae verae_ (true spiders) or _Araneae theraphosae_
(theraphosid spiders.)
Now these two kinds of spider may readily be distinguished by a single
easily observable characteristic, the nature of the mandibles or
_chelicerae_; but it is necessary to describe the spider’s mandibles
before the difference can be appreciated.
Their nature is perhaps best explained by saying that each mandible
is not unlike a penknife with a single small blade, rather more than
half open when in use, closed when at rest. The handle of the penknife
is certainly in most cases very short and thick, and the blade not
really a blade at all, for it has no cutting edge, but is a “fang” or
piercing instrument generally somewhat curved, and with a sharp point.
The “blade” is, moreover, perforated by a tube which comes from the
poison-gland, situated in the thickened “handle,” or in the spider’s
head, so that poison can be forced into the wound which it inflicts.
Now take two penknives with the blades half open and hold them so that
they hang with the hinge downward and with the blades directed towards
each other; it is clear that the blades may be made to pierce an object
situated between them by moving the handles laterally, the object being
attacked simultaneously on either side. This is the arrangement in the
true spiders, whose jaws move sideways, though they do not always hang
perpendicularly, but are more often somewhat slanted forwards.
To represent the jaws of a theraphosid spider the penknives must be
arranged differently. Place the handles horizontally and parallel to
each other, with the blades directed downwards and also parallel. They
will now work not sideways, but up and down, and both fangs will pierce
the victim from above. In a word, the true spiders have jaws which can
be separated or brought together, and which tend to meet in the object
into which they are plunged, while the jaws of theraphosid spiders work
in parallel vertical planes, and strike downwards.
All the spiders which have so far concerned us are _Araneae verae_,
and we have incidentally had occasion to note some of the principal
families of that division—Epeiridae (or Argiopidae as some prefer to
call them), Theridiidae, Agelenidae, Thomisidae, Lycosidae and Attidae.
Indeed there is only one theraphosid spider that there is the least
likelihood of our coming across in this country. Their true home is
in hotter climes, and though stragglers from their army are not rare
in the warmer portions of temperate regions, they abound only in
tropical countries. They include the “Trap-door” spiders, common in
the Mediterranean region and in many other widely distant parts of the
world, and the great “Bird-eating” spiders of the tropics—the spiders
which are quite wrongly but universally alluded to in America as
Tarantulas.
The single British example is well worth the study of any reader who is
fortunate enough to come across it. But he must first catch his hare,
for _Atypus affinis_ (or _piceus_ as it used to be called) does not
grow in every hedge-row, nor is it easy to find it where it does occur.
Most of the localities recorded are in the south of England. It is a
thick-set dark-coloured spider about half an inch in length, and with
very thick, powerful mandibles, which, as we have seen, work vertically.
Its nest is a loosely-woven tubular structure, which partly lines a
more or less vertical hole in the ground and partly lies exposed on the
surface, but which does not present any obvious opening for entrance
and exit.
The situation chosen is generally a sloping sandy bank covered with
vegetation. The burrow is about eight inches in depth and about three
quarters of an inch in diameter. Near the bottom it narrows and then
expands into a somewhat wider chamber where the spider lives and
constructs its egg-cocoon. The portion of the tube above the ground is
sometimes longer but more often shorter than the buried portion, and it
tapers to a closed end.
Mr Joshua Brown, who first found this spider near Hastings in 1856,
took home several of the tubes with the spiders inside. He could find
no opening, and though the spiders moved up and down the tubes they
did not emerge. On tearing a tube open he found no remains of insects
inside, but in one case he came across a worm, partly within, and
partly outside the lower part of the tube, and apparently partially
devoured by the spider.
The same species is not rare in France and M. Simon’s observations on
it closely agreed with those of Mr Brown. He believed that the spider
chiefly depended for its food on earthworms which, in the course of
their burrowings, came casually into its neighbourhood. Since these
observations, however, considerable light has been thrown on the habits
of the spider by Enock, who found colonies on Hampstead Heath and near
Woking. His investigations extended over several years, and wonderful
patience was needed before the secrets of this curious animal were
divulged.
It appears that the female, when once established, never leaves the
nest at all! The aerial portion of the web was always a puzzle, but now
we know, thanks to Enock, that it constitutes the whole hunting ground
of the spider. Like promises and pie-crust it is apparently made to
be broken. If it is accidentally brushed against by a passing insect
the spider is instantly aware of the fact, rushes to the spot, and
transfixes the intruder with its powerful mandibles. It turns on its
back to do this, and strikes the insect from behind, afterwards pulling
its prey through the weft and into the tube by main force. It drags it
to the bottom of the tunnel, makes sure of its death, and immediately
returns and repairs the rent.
Insects were held against the tube, and the spider, if hungry, accepted
them at once; if replete however, it always gave a tug at the tube,
which retracted a portion of it into the burrow—a curious action
which Enock quite learnt to interpret as the “I don’t want any more”
movement.
The males made nests exactly like the females, but shallower, and they
left them to search for their mates, leaving the ends open. On finding
a female nest, they “serenaded” by tapping with their palps, and after
some delay, tore open the web and entered. By and by the female came
up and repaired the rent, first pulling the edges together with her
jaws and then uniting them with silk from her spinnerets. In one case
nothing more was seen of the male for nine months, when his empty skin
was observed at the end of the tube. After nine months of connubial
bliss his consort had devoured him!
In the autumn and spring, eggs and newly-hatched young were often found
in the nests. Late in March a small hole, 1/16 inch in diameter, was
noticed at the end of some of the webs, and presently the young began
to emerge—never to return to the nest. They immediately climbed the
highest objects at hand, and some were seen to be carried off by the
breeze.
Enock found, by an ingenious experiment, that the sand which is
incorporated in the aerial part of the tube—no doubt to render it
inconspicuous—is obtained from within, and not from outside the nest.
Carefully covering the exposed web, he powdered the ground all round
it with red brick-dust, but the particles which the spider embedded
in the web were of brown sand, evidently obtained from the bottom of
the burrow and not from the surrounding surface. But in the case of
some newly-dispersed young spiders he was able to see this operation
performed. The first part of the nest to be made was the aërial
portion, at the foot of which the digging was commenced. Particles of
sand were brought up in the jaws of the young spider and pushed into
the weft of the tube. Occasionally the jaws were thrust through the
delicate web and particles from without were seized and _pulled_ into
the silken fabric.
It is sad to have to relate that such young spiders as did not emerge
from the web within a reasonable time were devoured by their unnatural
parent. It sometimes happened that a change of weather rendered it
unsuitable for the departure of the young, and in this case the mother
closed up the exit-hole, and retired to feed upon her offspring! Thus,
though there were as many as a hundred and forty in a brood, a good
many perished at the outset, and the ants in the surrounding soil
accounted for some of the rest.
The Atypidae form a small outlying group of the Theraphosid spiders and
are able to live in colder regions than most of their relatives. The
great bulk of the division belong to the family Aviculariidae.
Some of the Aviculariidae are not unlike Agelena in their mode of life,
spinning a dense sheet-web terminating in a tube, and entrapping
their prey. Far the greater number, however, as far as their habits
are known at all, are earth dwellers, either inhabiting more or less
complex burrows of their own, or sheltering under stones or in chance
cavities by day and emerging at night to seek food in the immediate
neighbourhood of their hiding-places. Some of them are quite small, but
the majority are large robust spiders, of formidable appearance. The
largest known spider, _Theraphosa leblondi_, is found in South America,
and its body measures more than three and a half inches in length.
Few spiders have attracted more attention than the fabricators of the
curious “trap-door” nests, which are common in the Riviera, and indeed
in all the countries bordering the Mediterranean. But abundant though
they are, they are extremely difficult to find, and it is generally
only by chance that their existence is detected.
The Tarantula occasionally closes the mouth of her tunnel with a sheet
of silk in which are encrusted the _débris_ of insects or particles of
soil. She does this at the time when she is spinning her cocoon and
any intrusion is particularly inopportune, but she does it also on
other occasions which are not so easily accounted for. A reason which
would naturally occur to us would be the exclusion of excessive rain or
excessive sunshine, but the facts, unfortunately, do not accord with
this explanation.
Now, however desirable occasional closure may be, a permanent door
would hamper the tarantula in her hunting operations, but the habits
of the trap-door spider are different, and she closes her retreat
with a wonderful hinged lid or “trap-door.” And the commonest form
of trap-door is also the most perfect, being thick and tapering, and
fitting accurately into the bevelled mouth of the tube like a stopper
in the mouth of a bottle. It is made of alternate layers of spider
silk and earth, and is free for more than half its circumference, the
remaining portion of the surface disc being attached to the side of the
tube by a flexible hinge of silk. Moggridge dissected the door of a
full-sized tunnel into fourteen graduated discs. The smallest—and of
course the lowest—represented the first door ever made by the spider,
and the successively larger discs indicated the stages at which its
increasing size rendered an enlargement of the tube—and therefore of
the door—necessary.
The spider always interweaves vegetable matter from the
neighbourhood into each new disc, so that, as a rule, it is entirely
indistinguishable from its surroundings when closed; and not only
_dead_ vegetable matter, for if the tube is situated amongst moss, moss
grows upon the lid. From our previous experience, however, we shall
not be surprised to find that blind instinct and not forethought is
responsible for this action. Moggridge removed the lid of a tunnel
and also cleared the ground immediately round it of all vegetation;
nevertheless, when the spider made a new door, it covered it with moss
taken from the undisturbed vegetation beyond, so that the trap-door
was now conspicuous as a green oasis in a sandy desert! And on another
occasion a spider interwove fragments of scarlet fabric left purposely
at hand into the lid of its tunnel. It is clear, therefore, that the
decoration of the door is due to an instinct which impels the spider
to utilise any material of the neighbourhood without any regard to the
effect produced.
The tube is densely lined with silk, which affords its architect a
secure foot-hold, and if any enemy attempts to open the lid from
without, the spider resists with all its strength—which is not
inconsiderable—clinging on to its under surface with its front legs
and jaws, while the claws of its other feet grasp the silken walls of
the tube.
The other type of trap-door is less interesting and much more
elementary, consisting simply of a wafer-like sheet of silk mixed with
earth and vegetable matter, but it is a curious fact that while all
known trap-door nests of the cork type are simple tubes, the burrows
with wafer doors are often much more complex. In some cases there
is a branch tube, like that constructed by _Lycosa picta_, leaving
the main tunnel at a depth of some three inches, and reaching the
surface perhaps two inches away from the trap-door, so that the whole
excavation is +Y+-shaped. This branch tube is permanently closed
by a thin sheet of silk and earth, which, however, it would not be
difficult to break through if it were urgent for the spider to escape
while the enemy was exploring the main tunnel.
But a more interesting case is the occurrence of another trap-door
some way down the tube. If the tube is unbranched, this forms merely a
second line of defence if the outer door is forced, but in the case of
a branched tube the additional door hangs at the fork of the +Y+,
and is so shaped as to form a perfect valve, so that the spider, by
holding it against one or the other side of the tunnel, can connect the
bottom limb of the +Y+ with either fork at will, leaving to the
intruder a beautifully smooth-lined tube to explore, with no hint of
the possibility of escape in other directions.
There are sometimes other complications in the ramification of the
tube, but these need not detain us. Each species of spider adheres to
its own particular type of architecture, and may safely—in a given
neighbourhood—be identified by its nest.
As with the Lycosidae, the burrowing is all done by the mandibles,
but here the first joint—the handle of the penknife—is of more
importance than the blade or fang. Indeed the burrowing species of the
Aviculariidae may be distinguished from the rest by their mandibles,
which are provided in front with a _rastellum_, or row of teeth for
digging. A trap-door spider, then, does not go to work like a rabbit,
or a terrier, scratching and kicking away the earth as it digs; it
laboriously dislodges particles of soil with its powerful mandibles,
and carries away the loosened fragments to deposit them at a distance.
The trap-door spiders of the Mediterranean region are nocturnal
creatures, and little is known of their habits. Erber relates that a
species found in the island of Tinos comes out at night, fixes open the
trap-door with a few threads, and spins a web near its nest to entrap
passing insects, clearing away any trace of it before the dawn. In the
case of some Chinese and also some Australian species observers allege
that they frequently wander from their nests in the day-time.
A Californian species was able to leave its nest when the trap-door was
weighted with three ounces of lead. On re-entering, it seized the edge
of the door with its mandibles, and, raising it slightly, inserted its
front legs. It then turned round and slipped backwards into the tube.
It always resisted the forcible opening of its door to the last moment,
when it let go and slid into the tube “as though going down a well.”
The larger Aviculariidae have acquired a reputation for feeding on
birds, and this has given rise both to their scientific and their
popular name—bird-eating spiders. Several travellers have stated that
they have observed them with birds in their grasp, and there is no
doubt of their ability to kill any small bird or mammal, though it is
probable that they seldom have the opportunity, for they spin no snare
in which birds may be caught. Even without the aid of their poison,
their jaws are so large and powerful that they may easily attain the
vital organs of small animals. Probably their staple food consists of
the larger insects.
They live in holes in the ground or in trees, or sometimes in the
fork of a tree-branch. In such hiding places they spend the hours of
day-light, emerging at night in search of food. Their large size and
uncanny appearance have attracted the attention of the collector, and
a great many species are known, but the fact that they chiefly inhabit
tropical countries has militated against any very extended study of
their habits, and the few items of information we possess are best
related with regard to the particular spider observed, and not taken as
necessarily characteristic of the whole tribe. There is little doubt
that they live for several years. McCook kept a specimen of _Dugesiella
hentzi_ in captivity for five and a half years, and he considered that
when it reached him it was at least a year and a half old, and probably
more. The same species has recently been made the subject of some very
interesting observations by Petrunkewitch, who obtained numerous living
specimens from Texas and kept them in captivity; unless carefully
packed, they bore the railway journey badly, and it was above all
things necessary to supply them with water.
The captives were fed on grass-hoppers, crickets, cockroaches and
wolf-spiders, but they ate sparingly, one grass-hopper sufficing for
three days in the summer, while in the winter hardly any food at all
was taken.
The sense of touch is extremely well developed in these spiders, but
in sight, hearing and smell they are strangely deficient. No response
whatever, was obtained to either high or low notes. A cricket sang for
hours quite close to a spider which had been kept hungry for several
days, without attracting any attention. It is very remarkable, by
the way, that insects show no instinctive dread of these formidable
creatures, not attempting to keep at a distance, and indeed frequently
running over them in trying to find a way out of the cage. Nor do the
spiders seem to be at all guided by smell; they evince no knowledge of
the presence of insects which emit a strong odour, nor do they react
to such tests as those to which the garden-spider was subjected unless
strong irritants such as chlorine are employed, in the perception of
which it is perhaps unnecessary that smell in the strict sense should
take any part.
They have eight eyes—two of them round and rather business-like in
appearance, and the others oval or pear-shaped—and they are very
sensitive to light, retreating at once from the direct rays of the
sun or from a light flashed on them, but they do not appear to _see_
anything at all, recognising neither friends nor enemies by sight,
however close at hand. It was far otherwise with a wolf-spider in the
same cage. Running towards the Dugesiella it was clearly aware of it at
a distance of several inches, and could not be persuaded to approach
nearer. But the supremacy of the sense of touch is most striking when
the spiders are courting. When the male is seeking the female he seems
quite unaware of her proximity unless he accidentally brushes up
against her. If he loses contact for a moment he is quite at sea and
wanders blindly about, turning, perhaps, to the left when the least
motion to the right would bring them together again. This frequently
happens when he has accidentally touched the female with one of the
hind legs. He immediately turns about, and if she is still there, all
is well, but if she has chanced to move out of reach, he is quite at a
loss. Neither sight nor sound nor smell guide him, but touch only. The
delicacy of this sense, however, is quite remarkable. He seems to be
aware at once of the nature of the object which touches him, assuming
a threatening attitude if the touch is hostile, or pouncing instantly
if hungry and the touch is that of a passing insect. If, however, the
insect is lucky enough to escape, it is in no danger of pursuit.
As in the case of many spiders—though by no means of all—his courting
is not unattended with peril. The tragic fate which sometimes overtakes
the male spider has so hit the popular imagination that there is a
general impression that the female spider is a confirmed misanthrope
and desires the life of any suitor bold enough to approach her. Not at
all! We have simply to remember that spiders are carnivorous and prone
to cannibalism. If the female happens to be hungry she makes no nice
discrimination between an amorous male and a succulent grass-hopper;
if replete, she may find time for the play of softer emotions. The
male of _D. hentzi_ appears to be more or less prepared for a hostile
reception on the part of the female, for the thighs of his front legs
are furnished with spurs at their extremity and with these he holds
back and renders powerless her threatening fangs.
There is no doubt that the spider’s delicate sense of touch resides in
the hairs with which both body and limbs are thickly clothed. They are
of various kinds—fine hairs, bristles, and stout spines—and many
of them are supplied with nerve-fibres at the base. The finer hairs
are probably not sensory, and they are, in the case of some Avicularid
spiders very easily shed, and have a strongly irritant action on the
hand that touches them, not unlike the sting of a nettle.
It is not at all unusual for one large Avicularid spider, _Psalmopoeus
cambridgii_, to be brought over to England in cases of bananas from
the W. Indies. Mr James Adams of Dunfermline has kept two specimens
alive for a considerable time. The first specimen lived in captivity
for two years and nine months, during which it moulted five times but
grew very little in size. Arriving in September, it was at first fed
on flies, and in a few weeks, when these began to fail, it accepted
beetles, consuming about three a day. In November, even these insects
were difficult to obtain, and recourse was had to cockroaches. At first
about three cockroaches a week were eaten but the number decreased
until, in the middle of March it ceased feeding altogether, and on
April 13 it cast its skin. It moulted again in October, and twice a
year for the rest of its life—in spring and autumn. During six months
it took no food at all, and very little for four months previously. At
the last moult but one it lost a limb, which however, reappeared when
the spider again changed its skin, though it never attained the proper
size.
With spiders, as with insects, moulting is a very serious matter,
involving much more than the mere casting off of an external coat. If
all does not go well limbs may easily be lost in the operation, nor is
it rare to meet with instances in which the animal has perished in its
unsuccessful attempt to discard the old integument.
Mr Adams’ second specimen was kept alive for three years and ten
months. It moulted only once each year—in June or July—and it died in
the act of casting its skin. In the case of these spiders, also, it was
noted that insects supplied to them as food displayed no fear whatever.
There were always a few cockroaches in the same box, and they were
often observed actually with the spider in its nest, but no notice was
taken of them unless their host chanced to be hungry. A photograph of
this spider is given in the Frontispiece.
It is an interesting fact that many of the Aviculariidae of Southern
Asia and Australia possess a sound-producing apparatus which is
entirely lacking in African and American forms, but this is a subject
which deserves a chapter to itself.
CHAPTER XII
STRIDULATION
Many of the Arthropoda—the large group which includes insects and
crustaceans as well as Arachnida—are able to produce sounds, a fact
familiar enough in such insects as crickets and grass-hoppers. As,
however, the breathing apparatus of these animals is entirely different
from that of mammals and has no connection whatever with the mouth
and alimentary canal, the mode of sound production is not at all the
same. Instead of setting vocal chords in vibration by the expulsion of
air through the larynx, insects “sing” or “chirp” by rapidly rubbing
together certain specially roughened surfaces, which constitute what is
called a “stridulating organ.” In crickets, for instance, each tegmen
or wing-cover is provided with a kind of file, and when the wing-covers
are rapidly vibrated, the edge of each rubs against the opposite file,
and a loud shrill sound is produced.
The stridulating apparatus is by no means always in the same place; the
thorax may rub against the abdomen, the leg against the wing-cover,
or one of the mouth appendages against another. Nor are the sounds
produced always audible to human ears; at all events there are many
creatures with what appear to be very well developed stridulating
organs whose note has never yet been heard by any naturalist, but there
are doubtless numberless sounds beyond the range of our hearing, which
is limited, like the keyboard of a piano.
Now such a stridulating apparatus has been detected in many spiders,
and always in one of three situations—either between the two parts
of the body (cephalothorax and abdomen) or between the palps and the
mandibles, or between the palps and the front legs. In some of the
Theridiidae the hind end of the cephalothorax is roughened and fits
into a sort of socket in the abdomen which is provided with parallel
ridges, so that when the abdomen is vibrated the two surfaces are
rubbed together, but no one has yet heard a sound produced by these
spiders. The stridulating Aviculariidae, however, are easily heard, the
sound in some cases being described as a kind of whistle,—in others it
has been said to have the effect of shot dropping upon a plate.
There are two quite distinct purposes for which sounds may be produced;
they may either serve as a call from one sex to the other, or as a
warning to intruders. Obviously the first purpose requires a sense
of hearing in the sex appealed to, and it is interesting to note
that in the Theridiidae, which are among the spiders which show some
appreciation of sound, the organ is well developed in the male only,
being rudimentary or altogether absent in the female, while in the
Aviculariidae, which appear to be quite deaf, both sexes possess it
equally. In them its function is probably to warn off its enemies—a
purpose for which it is not at all necessary that the spider itself
should hear it.
Sometimes sounds have been quite wrongly attributed to spiders; there
is, for example, an Australian species widely known among natives
as the “barking” or “booming” spider, for no better reason than
that the spider has been found in the day-time at a spot where the
booming was heard at night. This case was investigated by Professor
Baldwin Spencer, who found that quails were really responsible for
the sounds with which the spider was credited. The creature could,
however, achieve a kind of whistle by rubbing its palps against its
mandibles. Its stridulating apparatus was of the type common among
the Aviculariidae. Its principle is that of the musical box, where
nail-like projections on a barrel strike against the teeth of a metal
comb, except that the barrel is stationary and the comb is moved up and
down against it. The barrel is here represented by the first joint of
the mandible which is beset on its outer side with spines. The inner
edge of the first joint of the palp is furnished with “keys” which
are rubbed against the mandible spines when the palps are vibrated.
These keys are very curious structures. They are of various lengths,
and their shape will perhaps be understood when it is said that a
tolerable model of one would be obtained by taking a flat iron bar,
sharpening it at the end, and then so twisting it in the middle that
the flat surface of one half is at right-angles to the flat surface of
the other half. Its appearance therefore varies according to the point
of view, the narrow edge of one half and the broad edge of the other
being visible at the same time. A moment’s consideration will show that
this torsion is calculated to give great rigidity to the keys, for when
the outer half is struck on the flat surface the inner half opposes
its greatest diameter to the shock. A similar structure is found in
all the Theraphosid spiders which are able to produce a sound, though
sometimes the “keys” are on the mandibles and the spines on the palp.
[Illustration: Fig. 11. Three “keys” of a stridulating organ, after
Spencer.]
In Staten Island there is a wolf-spider—_Lycosa kochi_—which is known
as the “purring” or “drumming” spider because of a curious habit which
the male has, at mating time, of rapidly drumming on the dead leaves in
a wood with its palps. It runs hither and thither over the ground as
if in search of something, pausing at short intervals to “purr,” and
the sound had frequently been heard and correctly attributed to the
spider before the way in which it is produced was discovered. In this
case it is probable that the production of sound is not the object of
the spider at all, for we have no evidence that wolf-spiders hear. On
the other hand rapid tapping with the palps is a very characteristic
action with male spiders at mating time, and it is easy to believe that
contiguous dry leaves would conduct vibrations to a female at some
distance away and inform her of the presence of the male. Just so, as
we have seen, our English Theraphosid announces his arrival by tapping
on the exposed part of the nest of the female.
CHAPTER XIII
THE SPINNING APPARATUS, AND THE FEET
Seeing that the possession of spinnerets is a characteristic of all
spiders, and that a great deal of the interest attaching to their
life-history arises from their spinning operations, any account of
the group, however brief, would be incomplete without some attempt to
describe these remarkable organs.
Among the spiders to which the attention of the reader has been
directed, some have been highly accomplished spinners, constructing
complicated snares, retreats and egg-cocoons, while in the case of
others the spinning work is very meagre and employed chiefly for the
protection of the eggs. As might be expected, the organs attain a very
much higher development in some spiders than in others, and the most
complex of all are those of the Epeiridae, the constructors of the
circular snare.
Now in the first place it is rather striking that the spiders with the
most conspicuous spinnerets are by no means the most able spinners. The
“bird-eating” spiders are a case in point, for they spin very little,
yet two of their spinnerets are much more obvious than anything Epeira
has to show, for they protrude behind the body and strike the eye at
the first glance. Indeed excessive length has nothing to do with
complexity but is found wherever a wide sweep is necessary in laying
down the threads—as we saw in the case of Agelena, when constructing
its sheet-web.
Roughly speaking, the spinnerets are very mobile finger-like
projections, generally situated under the hind end of the abdomen and,
bearing more or less numerous tubes from which the silken threads
proceed. The usual number of spinnerets is six, but there is a pretty
wide range, one group of spiders having only two, while a few possess
eight.
The spinnerets, then, are only the bearers of the actual tubes which
emit the silk. The distribution of the tubes themselves is different
in the different kinds of spiders, but it is usually possible to
distinguish two kinds. There are generally present a large number of
very fine cylindrical tubes or “spools” and a few conical tubes of much
larger base, which are called spigots. Each of these orifices, whether
on spool or spigot, is connected by a fine tube with a separate silk
gland, or organ for manufacturing silk, situated within the spider’s
abdomen. Epeira has about 600 of such glands, each with its own
terminal spool or spigot, and the large number of these tubes has given
rise to a misconception that is very widely spread—namely that the
spider’s line, fine as it is, is “woven” of hundreds of threads of very
much finer silk. This is not so, as we shall presently see.
Though Epeira has some 600 silk-glands, it has only five different
_kinds_ of gland, manufacturing silk of different properties. No other
family of spiders has so many, though two other kinds of gland have
been found in less elaborate spinners. Within the spider the silk is
fluid but it solidifies on meeting the air, each thread hardening as it
emerges though still continuous with the fluid contents of the gland,
so that the drawing out of a silken thread is just like the operation
so familiar with the glue-pot, or with spun glass, except that the
hardening is not due to cooling but to exposure to the air. This
general description will, it is hoped, make an account of the organs in
Epeira more comprehensible.
The spinnerets of Epeira are so small and inconspicuous that their
disposition is not very easy to make out. When not in use they form
a tiny cone under the tip of the abdomen, and only four are visible,
their free ends being so brought together as entirely to conceal a
small central pair. There are really, then, three pairs of spinnerets
which we may call at once the anterior, median and posterior pairs,
though when at rest only the anteriors and posteriors can be seen.
If the spider is observed with a pocket-lens as it crawls about in a
glass tube it will be noticed that the spinnerets are capable of great
mobility. Their ends can be separated or brought together, or they may
be made to rub against each other or against the sides of the tube.
The anteriors and posteriors, moreover, are two-jointed though the
medians consist only of a single joint.
So much can be seen without any great magnification, but the microscope
will be necessary if a complete understanding of their mechanism is to
be arrived at. What it reveals will now be briefly described, and will,
it is hoped, be made tolerably clear by the accompanying figures which
are simplified by the omission of a large number of bristles which tend
to hide the essential structure, and by a great reduction in the number
of “spools,” though the spigots are all indicated.
The anterior spinneret (that nearest the head end of the animal) is a
sort of cone, divided into a large basal joint and a small terminal
joint. The latter bears on its inner side a single spigot (fig. 12 _a_)
and is crowned with a battery of spools, about a hundred in number.
The median spinneret has three spigots, two at the tip and one on the
inner side (fig. 12 _b_), and about a hundred spools, mostly on its
inner surface.
The posterior spinneret is divided very obliquely into two joints, so
that the terminal joint extends much lower down on the inner than on
the outer side. It has five spigots in groups of three and two, and
again there are about a hundred spools.
Now the point that I wish to make clear is that there is no
interweaving of the output of these various spools and spigots. At the
moment of emission the threads are adhesive, and can be made to stick
to the glass or to one another, but they are not in any sense either
fused or interwoven. For ordinary operations the brunt of the work is
borne by the spigots marked _a_ in the figure, sometimes reinforced
by silk from the spigots on the median spinnerets marked _b_, the
functions of all the other spools and spigots being special and
occasional. For instance, when Epeira is laying down a foundation line,
this is what happens. The spider sits down, so to speak, on a twig,
separating its spinnerets and rubbing them on the surface. As it raises
its abdomen a multitude of little threads are seen merging into what
appears to be a single line.
[Illustration: Fig. 12. View, from the inner side, of one of each of
the three spinnerets of _Epeira_. _A_, anterior; _B_, median; _C_,
posterior spinneret.]
In reality the line is double, emerging from the spigots (_a_) on
the anterior spinnerets, and it can easily be separated into two—and
two only—any where along its length. The multitudinous spools have
emitted short lengths of silk to anchor the foundation line at its
commencement, but they are then closed and have no share in the
ever-lengthening line as the spider lets itself drop or crawls away
to attach it to a new spot. One of their uses, then, is to anchor
the main lines from the spigots to external objects, but they have
another function not less important. Everybody has seen a garden-spider
trussing up a captured fly. It is held in the jaws and front legs and
slowly revolved while with its hind legs the spider draws out bands of
silk from the spinnerets and swathes it like a mummy. No silken rope,
this, of fused or interwoven threads, but a broad band, every strand
of which is separate and distinct and proceeds from a different spool.
Two or three hundred fine threads wound simultaneously round the insect
form a much more effectual winding sheet than would a single cord
composed of them all.
So far we have accounted for the spools, and for one pair of
spigots—those on the anterior spinnerets. The lower spigot (_b_) on
the middle spinneret often assists in laying down a foundation line
when extra strength is required. In that case the line is fourfold, and
can easily be split into four along its whole length, the threads from
the middle spinnerets being rather finer than those from the anterior,
but composed of the same kind of silk.
There remain seven pairs of spigots whose function has still to be
explained, two on the middle and five on the posterior spinnerets. The
three which are clustered together on the posterior spinneret do not
form _silk_ at all, that is, the material they emit does not harden on
exposure to the air but remains fluid and adhesive. When the spider is
spinning the “viscid spiral” of its web it is from these spigots that
the sticky matter oozes, enveloping the true silken lines and presently
resolving itself into little globules in the manner already described.
The remaining spigots—two on the middle and two on the posterior
spinnerets are employed only in spinning the egg-cocoon, and the silk
they produce is unlike that used in making the snare, being much
stronger and less elastic, and—in the case of the garden-spider—of
a yellow colour. In the occasional attempts which have been made to
substitute spiders for silkworms as commercial silk producers, it is
only this cocoon silk that has given any considerable results, the
produce of the other glands being far too frail for profitable use.
Such attempts, however, have always failed, principally for a reason
quite unconnected with the particular nature of the silk, namely,
the difficulty of keeping the spiders in captivity. It is a simple
matter to supply dozens of silkworms in the same box with mulberry
leaves, but spiders require separate compartments or they will fight
and devour each other, and the provision of suitable food for them is
such a troublesome matter that it has proved quite impracticable on a
commercial scale.
We have incidentally seen that there are quite a number of different
operations in which the spinning apparatus takes part. There is the
line which most spiders lay down as they wander, and which secures
them from the danger of a fall if they lose their footing; there is
the snare for catching prey, the nest or retreat, and the egg-cocoon,
and in addition, silk from the spinnerets may be used to enwrap and
paralyse captured insects, or to assist the young spider to migrate.
Since the Epeiridae perform all these operations, and are, moreover,
the most finished of snare-makers, it does not surprise us to find in
them the highest development of the silk glands and the most complete
battery of spools and spigots on the spinnerets. Many spiders, as
we know, make no snare at all, and in the case of some, very little
spinning is attempted beyond the manufacture of a rather rudimentary
covering for the eggs. Naturally a less complex spinning apparatus is
required, and we accordingly find that jumping spiders, for instance,
have only about fifty silk-glands comprising three different kinds of
gland, while the glands found in such of the large Aviculariidae as
have been examined have been all alike.
There is in some spiders a spinning organ, not to be found in
Epeira, which deserves a passing notice. It does not take the place
of spinnerets, of which the usual three pairs are present, but it
is situated in front of them, and only occurs in the female of the
species. Its peculiarity is that the silk does not emerge from
projecting spools; but through fine holes in a sieve-like plate, called
a _cribellum_, which is flush with the surface of the abdomen. It has
no mobility, therefore, and the threads from it have to be combed out
and distributed by the spider’s hind leg. For the better accomplishment
of this purpose there is a special comb of stiff hairs or bristles,
called a _calamistrum_, on each of the fourth pair of legs.
The web of these spiders is not unlike that of Agelena, but of a rather
finer texture, and it can be seen, on magnification, to consist of
an irregular ground-work over which have been spread wavy bands of
excessively fine silk, combed out from the orifices of the cribellum
glands. Some of these cribellate-spiders, of the genus _Amaurobius_,
are not uncommon in our cellars and out-houses; their bodies are of
stouter build and their legs much shorter than those of the common
house-spider.
We have no space for anything approaching a full description of the
anatomy of spiders, but there is one other point of structure of which
the reader has been promised some account. Attention was directed to
the fact that while some spiders are helpless on smooth perpendicular
surfaces unless they have lines to cling to, others can run with ease
upon the walls or even the ceiling, of a room.
[Illustration: Fig. 13. Foot of Jumping Spider (on left), foot of
Garden Spider (on right).]
The last joint or _tarsus_ of the spider’s leg is very different in
the two cases. It always terminates in claws—either two or three—so
that any species can make some show of climbing where the surface is
rough and there is anything to cling to, but to obtain a hold on a
polished surface it needs a special contrivance. This takes the form
of a pad of curiously modified hairs, called a _scopula_. The hairs
are club-shaped, narrow at their stalk and swelling towards the tip,
and their clinging power seems to be due to a viscid secretion. The
foot of any jumping spider will show this structure well. Epeira has no
scopula, and its climbing is always laborious unless it has a thread
to cling to, but it is supreme as a rope walker, treading daintily on
the most delicate threads, mounting a line “hand over hand” with great
agility, and manipulating the silk in its various spinning operations
with unerring skill and facility.
CHAPTER XIV
THE ENEMIES OF SPIDERS
When one comes to consider the multitudinous risks to which a spider is
exposed during the whole course of its life it seems at first a little
surprising that the whole tribe has not long ago been exterminated.
Spiders continue to flourish, however, and it is very clear that
however careless Nature may be of the individual she is extremely
solicitous about the race.
The infant mortality among these creatures must be appalling. There is
first their cannibalistic propensity to be reckoned with. Newly hatched
spiders while still within the cocoon seldom attack each other, but as
soon as ever each sets up for itself, no quarter is given. It often
happens that members of a brood of sedentary spiders spin their first
snares in close contiguity, and if food is scarce they eat one another
without compunction. It is said that a few individuals of a brood may
be reared to maturity on no other food than their sisters and brothers!
The case of the survivor of the “Nancy Bell” in the Bab Ballads would
be exceedingly commonplace in the aranead world. We have seen, too,
how, on occasion, _Atypus_ will devour her young if they do not leave
the nest with due expedition. Then if the weather conditions chance to
be unfavourable just at the period of departure from the cocoon broods
are liable to perish wholesale, washed away and destroyed by deluges of
rain; myriads, too, must be carried out to sea in the course of their
ballooning operations, and never come safely to land.
But the mortality is probably even greater at a still earlier stage,
for hosts of spiders’ eggs never hatch at all, and this for two
reasons. In the first place, the silk of spiders is a favourite
material with many birds for the lining of their nests, and many of
them use the cocoons for this purpose. Secondly, there are numerous
Ichneumon flies which attack and parasitise spiders’ cocoons, piercing
them with their ovipositors and laying their eggs inside. The eggs of
the Ichneumon fly hatch first and feed upon the eggs of the spider.
Two such flies are known to attack the cocoons of the garden-spider,
and not a single spider will emerge from a cocoon thus parasitised.
The spiders whose cocoons are most subject to these attacks belong,
as might perhaps be expected, to the sedentary groups, and the most
elaborate but unavailing precautions are often taken to render them
Ichneumon-proof. The cocoons of the peripatetic wolf-spiders have never
been observed to be parasitised.
Even if a spider has survived these early perils there are still many
dangers ahead. During its period of growth it has to moult some eight
or nine times, and the operation is at least as dangerous as, say, an
attack of measles to the human infant. For some time beforehand feeding
ceases, and the animal becomes inert and apparently dead, but presently
the integument splits, and out struggles the spider, pale and soft, and
leaving behind it not only the outer skin but the lining of most of
its alimentary canal and of its breathing tubes. Sometimes, as we have
said, it fails to extricate itself and dies; quite often it emerges
with the loss of a limb, which will reappear—reduced in size—at
the next moult. It is necessary to go into retreat for a time after
moulting, till strength has returned and the integument has hardened.
But the dangers of moulting, though not negligible, are insignificant
beside others to which the spider is exposed during its later stages,
nor is a prolonged dearth of food necessarily fatal, for, as we have
seen, a spider can fast for an astonishing time and yet retain its
health if it has a fair supply of water. But there are terrible
enemies at hand from which it has little or no protection. Birds,
of course, come first, for to most insectivorous birds spiders are
acceptable morsels. I have seen a hedge sparrow going conscientiously
over a trellis work and picking out all the spiders from the nooks and
corners. Then insectivorous mammals make no distinction between the
Insecta and the Arachnida, and often eat spiders with avidity, as also
will toads and lizards.
Moreover, Ichneumon flies do not confine their attention to cocoons,
but often attack well-grown spiders. They invariably lay their eggs on
one spot—at the very front of the abdomen, near the cephalothorax,
where the spider is powerless to dislodge them. The egg hatches out
to a grub which is a veritable “old man of the sea” on the spider’s
back, and there it remains until it causes the death of its victim by
feeding on the contents of the abdomen. Four such Ichneumon flies have
been found to attack the garden-spider, and no kind of spider seems
exempt. How they contrive to deposit their eggs in the proper place
without great danger of themselves falling a prey to their victims
is a mystery. To venture into a garden-spider’s web for the purpose
would seem a fool-hardy proceeding. The actual deposition of the egg
has seldom been witnessed, but in one of the few cases that have come
under observation the spider made little resistance and appeared quite
demoralised. It was hanging from a thread, down which the Ichneumon fly
was seen to crawl. When it reached the spider the latter dropped an
inch lower on two or three occasions but then remained passive, and the
parasite on nearing it, turned round, backed down the line, and with
great care and deliberation attached an egg at the usual spot.
But no enemies of spiders are more terrible than some of the solitary
wasps, and gruesome indeed is the fate of any creature that falls
into their clutches. The social wasps often capture spiders to feed
their young but in their case the proceeding is summary and without
any finesse. They merely catch a spider, sting it to death, cut it
to pieces with their jaws, and feed it into the mouths of their
expectant grubs. The treatment is brutal enough, but at all events it
is expeditious. Now the solitary “digger” wasps never see their young.
They make cells, either by burrowing in the ground or by agglomerating
particles of mud or gravel, and in each cell is placed an egg together
with sufficient food to last the grub which hatches out for the whole
of its larval existence. The mother will not be at hand—as is the
social worker-wasp—to supply new food as required, and it is therefore
necessary so to arrange matters that the food provided may retain its
fresh condition for at least a fortnight. On the other hand the victims
must be deprived of all power of motion, otherwise the egg will stand
a great chance of being displaced and crushed, and even if it hatches
it will be unable to commence its meal upon the struggling spider.
Now in the whole range of animal instinct there is nothing more
remarkable than the manner in which the solitary wasps have learnt to
solve this problem. The solution lies in so stinging the victim that
it is paralysed but not killed, and though quite unable to move, it
neither shrivels nor decays, but remains perfectly sound and edible for
two or three weeks. To accomplish this result the wasp acts as though
it possessed a knowledge of the minute anatomy of its victim, and
knew to a hair’s breadth the position of the principal nerve ganglia
which control its actions. Into these it unerringly thrusts its sting.
But even accuracy of aim is not everything; there must be the finest
discrimination in the severity of the wound. A slight excess, and the
animal is killed; too timid a thrust will not destroy movement. When
the delicate operation has been successfully performed, the paralysed
spider is dragged into the cell, placed on its back, and an egg
carefully deposited at the base of its abdomen, after which the cell
is sealed up. Some wasps, instead of providing a single large spider,
store their cells with a number of smaller victims, all rendered limp
and motionless.
In attacking a spider the first action of one of these wasps is to
remove it from its natural environment. A garden-spider in its web, or
a burrowing spider in its tunnel are more or less formidable, but if
the one can be thrown down, or the other dragged forth into the open,
they are well-nigh defenceless. Therefore in attacking an Epeirid the
wasp first darts at it, seizes a leg, and attempts to jerk it out of
the web. If unsuccessful, the spider will now be on its guard, and the
wasp leaves it and tries the same manœuvre on another individual. Taken
by surprise, it is instantly thrown to the ground, and can then offer
no effectual resistance. Even the large “bird-eaters” fall victims to
these terrible foes.
CHAPTER XV
SOME CONCLUDING REFLEXIONS
In the foregoing pages we have been able to deal with very few out of
the vast number of known spiders; yet the examples we have chosen for
study are fairly typical of some of the more important groups, and
calculated to give a tolerably just idea of the general economy of the
tribe. In any case even such a fragmentary study as the present gives
us food for thought. There is a question which the writer has so often
been asked that he is inclined to deal with it in anticipation, though
perhaps he is wronging his readers in supposing that they desire to
propound any such conundrum. This question is: What is the _use_ of
spiders?
Now underlying this question there is surely a very unwarranted
assumption that all the myriad creatures which exist have, as a reason
for their existence, some reference to the activities and desires of
mankind. As far as it has any meaning at all it amounts to this: What
benefit does man derive from spiders? But it seems to take for granted
that some benefits must accrue to man from these creatures, or they
would not have the audacity to persist in living. Well, if the question
in this amended form is in urgent need of an answer, the reply must
be: very little if any. Certainly spiders prey as a rule on insects
and no doubt kill many which might injure us, and in the constant
battles between man and insect pests, instances have been recorded
where particular species of spider have fought on the side of man with
appreciable effect. But then they are as likely to devour our insect
friends as our insect enemies, impartially slaying the just together
with the unjust, so that little stress can be laid on their utility on
this score. Indeed there is quite as good a case to be made out of man
benefiting spiders as of spiders benefiting man, for his architectural
proclivities have provided some species with secure homes from which
most of their enemies—except man himself—are excluded, and where they
are sheltered from the storms which are so fatal to their relatives
outside, protected from extremes of temperature, and rendered so
independent of times and seasons that the number of broods they produce
in the year has increased. Whether a creature is useful or injurious
is entirely a matter of the point of view. There are several animals
with regard to which the opinions of the farmer and the gamekeeper are
diametrically opposed!
But if anything emerges from the study in which we have been engaged,
it is surely this fact: that wherever there is a niche in nature
capable of sustaining life, to that niche some animal will sooner or
later adapt itself without any reference to man’s desires or interests.
We have seen spiders, all built on the same ground-plan, so to speak,
and with the same essential organs, so modified in the details of
structure and inherited instincts as to be able to thrive under the
most diverse conditions. Think, for instance, of the water-spider
and the desert Tarantula, or consider the difference in mode of life
between the sedentary garden-spider and the hunting Attid.
Incessant competition in the struggle for life no doubt urged on
primeval spiders to strike out new modes of existence. Under slightly
novel conditions the best adapted or most adaptable survived and
were pioneers in the occupation of a new territory till the widely
different capacities and habits which we now wonder at were slowly
evolved.
Another point to ponder on is the wonderful complexity of the instincts
which govern the actions of spiders; the extraordinary operations
they can perform, entirely untaught, and of the object of which it is
impossible to believe they are aware. We have seen that, in the most
highly organised species, the sense organs—except perhaps that of
touch—are but moderately developed, and the power of memory, the basis
of intelligent action, but feeble; yet their inherited impulses suffice
for all ordinary emergencies, and recur with unfailing precision at
the proper periods of their lives. They are machine-like, perhaps, but
what extraordinarily competent machines! The light of what we call
intelligence burns low, but a glimmer of it can be detected here and
there.
If one comes to think of it, the egg of a creature of complex instincts
is a particularly wonderful atom; it contains not only the germs of all
the complicated bodily structure, but there are bound up in it also
the impulses that are to come into play at certain definite periods
only of the spider’s life-history. And these impulses are not mere
vague reminders that now is the time to spin a snare, or to weave an
egg-cocoon; they prescribe precisely how it is to be done, involving
perhaps a dozen different spinning operations in one unvarying order.
Viewed in this light, the germ of an insect or a spider would seem
in a sense to be more complex than that of an animal whose vague
instinctive impulses are under the direction of intelligence, and can
be carried out in a variety of ways according to circumstances.
One of the most surprising things about the egg of a spider is the
amount of _energy_ stored up in it. A bird’s egg, huge in comparison,
contains material sufficient to build up the body of a fledgeling just
sufficiently active to be able to accept from the mother that first
nutriment without which it will speedily die.
But turn back to the account of the tarantula-spider. Its egg is
small—perhaps the twelfth of an inch in diameter; yet it not only
produces a spiderling complete in form, and provided with all the
complex instincts of its tribe, but there is so much energy to spare
that, for months, without any new food-supply, the young spider
can lead an active life, frequently descending from and remounting
its mother’s back, and can even put forth silk on its own account!
The objects which a conjuror produces from a hat seem trifles in
comparison with the outcome of a spider’s egg—the actual material
seems astonishing from so small a source, but whence comes all this
surprising surplus of energy? Fabre suggests that it is supplied by
the direct rays of the sun, to which the Tarantula exposes in turn all
parts of the egg-cocoon.
All through their lives spiders seem to be gifted in a high degree with
the power of extracting the utmost value, in substance and in energy,
from their food. Consider the great Theraphosid spiders—the so called
bird-eaters. They have a massive body, and great muscular power to
sustain; yet they are never heavy feeders and can go for many months
without any food at all. And it is not as though they were dormant
during this period of abstention; their vital processes seem to be
going on as usual the whole time, and they are ready at any moment
to resent attack, or to employ their spinning organs during their
long fast. True hibernation, as we have seen, does not occur in this
group; if it did, there would be nothing remarkable in the occasional
long abstention from food. The vitality of a hibernating animal is
practically at a standstill; all its vital operations—breathing,
blood-circulation, muscular action—are reduced to the lowest possible
limit, and it very likely expends no more energy during its winter
sleep than it would during a day or two of active summer life.
But of such reflexions there is no end, and many such will doubtless
arise spontaneously in the mind of the thoughtful reader, and it is for
that very reason that the study of the life-history of any animal is of
such absorbing interest. It is not contended that spiders are any more
wonderful than any other group that might have been selected. There
is, of course, a special interest attaching to the study of animals
very much nearer to man in bodily structure and mental equipment, but
the endeavour to understand the actions and appreciate the outlook on
nature of creatures far remote from man, however unsuccessful, has its
own fascination.
And this is what the mere collector entirely misses. Collecting is
of course necessary, for a complete examination is never possible in
the living specimen, and moreover without examples kept as types for
reference we should lose our way in the multitude of living forms. But
as an end in itself it is of vastly inferior value. The writer will be
well content if he has succeeded in arousing the curiosity of some with
regard to the humble life that surrounds us, and in stimulating a few
who possess the requisite keenness and patience to add to our store of
knowledge by new observations of their own.
LITERATURE
Most of the large publications on the Arachnid fauna of different
countries give some preliminary account of the habits of spiders, but
the only considerable work entirely devoted to that subject is McCook’s
_American Spiders and their Spinning-work_ (Philadelphia, 1893). A
small but interesting book on _The Structure and Habits of Spiders_
was published ten years previously by Emerton (Boston, 1883). But the
reader who wishes to pursue further the study of some point to which
his attention has been called in the foregoing pages may desire to be
referred, for fuller details, to the original papers.
Many writers have described the spinning of the circular snare,
and indeed it is quite easy for any one to watch the operation for
himself; but McCook goes into the matter in great detail and figures
many interesting variants of its normal form. J. H. Fabre’s delightful
_Souvenirs entomologiques_ (Delagrave, Paris) have been issued at
intervals for many years past, and mostly deal with insects. In
Series 9, however, he has an entertaining chapter on “Les Epeires.”
That the “viscid globules” arranged themselves mechanically was first
demonstrated by C. V. Boys (_Nature_, xl, 1889, p. 250). The same
writer experimented on the sense of hearing in spiders (_Nature_,
xxiii, 1880, p. 149). The interesting paper by G. and E. Peckham on the
mental powers of spiders is to be found in the _Journal of Morphology_
(Boston U.S.A. i, 1887, p. 403.)
The aeronautic habit has engaged the attention of many arachnologists.
Blackwall dealt with it in various papers in the _Transactions of the
Linnaean Society_ between 1833 and 1841, but the most complete account
is to be found in McCook’s original papers which are summarised in his
book already cited.
With regard to the spinning operations of _Agelena_ the reader may
consult a paper by the present writer in the _Annals and Magazine of
Natural History_, August, 1891.
The habits of the Water Spider were first described by de Lignac in
a _Mémoire_ published in 1749. Since that date many writers, notably
Wagner and Plateau, have dealt with the subject. The paper by the
last named in the _Annales des Sciences naturelles_, 1867, p. 345, is
particularly worth reading.
E. Peckham deals with “Protective Resemblances in Spiders” in the
publication of the _Natural History Society of Wisconsin_ for 1889.
The reader interested in the habits of the Wolf-spiders must certainly
consult the chapters on “La Lycose de Narbonne” in Series 9 of Fabre’s
_Souvenirs entomologiques_.
The classical account by the Peckhams, of the love dances of jumping
spiders appeared conjointly with the paper by E. Peckham on “Protective
Resemblances” cited above.
For the habits of _Atypus affinis_ (or _piceus_) the reader is referred
to the very complete account given by Enock in the _Transactions of the
Entomological Society_ (London, 1885, p. 394) of observations extending
through several years.
The larger Aviculariidae have been dealt with in various papers by
Pocock, and the particulars given with regard to _Dugesiella_ were
taken from a paper by Petrunkevitch in the _Zoologischen Jahrbüchern_,
xxxi, 1911.
In the _Archiv für Naturgeschichte_, i, 1889, Apstein published an
admirable piece of research on the structure and function of the
spinning glands of spiders. He investigated the glands present in the
various families, and the particular arrangement of the spools and
spigots on the spinnerets.
A paper by the present writer in the _Quarterly Journal of
Microscopical Science_ for April 1890 continued this investigation, and
shewed the special operations in which the various glands participated
in the case of the Garden Spider.
INDEX
Aerial flights, 32
_Agelena_, 38-46
Agelenidae, 11, 38
_Araneae theraphosae_, 87
_Araneae verae_, 87, 89
_Argyroneta_, 3, 49, 50, 51, 52
Arthropoda, 6
Attidae, 4, 33, 52, 76-87
Atypidae, 93
_Atypus affinis_, 89, 121
Balloons, 34
Banana spider, 103
Barking spider, 107
Bird-eating spiders, 25, 89, 99
Body parasites, 123
Burrows, 63
Calamistrum, 118
Cannibalism, 33, 120
Carrying the young, 73
Characteristics of spiders, 4
Chelicerae, 10, 87
Cocoon, 12, 44, 64
Cocoon of _Agelena_, 44
Crab-spiders, 52
Cribellum, 118
Crustacea, 6
_Cyclosa conica_, 28
Darwin’s Pike, 22
_Desis_, 49
Drassidae, 11
Drumming spider, 109
_Dugesiella hentzi_, 99
Educability, 22, 27, 28
Egg parasites, 121
Enemies of spiders, 120
Energy stored in the egg, 130
_Epeira_, 3, 19, 112-116, 119
_E. diademata_, 13
Eyes of jumping spiders, 78
Feet of spiders, 119
Foundation lines, 13, 14, 16, 17
Garden-spider, 2, 13, 15, 19, 20, 23, 27, 39, 78, 121, 123, 126, 128
Gossamer, 36
Habits of _Agelena_, 38
_Atypus_, 90
Jumping spiders, 79
Tarantula, 69
Theraphosid spiders, 99
Trap-door spiders, 95
Harvest spiders, 8
Hearing, 23, 101
_Heteropoda venatorius_, 37
Hibernation, 2, 131
Hub, 13, 14
Huntsman spider, 37
_Hyptiotes paradoxus_, 31
Infant mortality, 120, 121
Instinct, 21, 22, 29, 46, 129
Jumping spiders, 4, 76-87
_Linyphia_, 3, 32
Love dances, 82-87
Lung-books, 10
_Lycosa kochi_, 109
_Lycosa picta_, 61
Lycosidae, 5, 33, 52, 58-76
Mammillae, 10
Marine spiders, 49
Mental powers, 20
_Meta segmentata_, 23
Mimicry, 55-58
_Misumena_, 54
Moulting, 104, 122
Notched zone, 13, 14
_Philodromus_, 54
_Phrynarachne_, 57
_Pirata_, 59, 66
Poison of spiders, 75
Poison gland, 88
_Psalmopoeus cambridgii_, frontispiece, 103
Purring spider, 109
Rastellum, 98
Recognition of cocoons, 66
Red spider, 8
Scopula, 119
Sight, 23, 60, 81, 101
Silk glands, 111, 112
Smell, 25, 100
Solitary wasps, 124, 125
Spigots, 111, 113-116
Spinnerets, 8, 110-118
Spinning apparatus, 110
Spinning glands, 111
Spinning operations, 117
Spools, 111, 113, 114, 115
Starvation, 122
Stridulation, 25, 105
Stridulating Keys, 107, 108
Tarantula, 68-74, 128
Tarsus, 119
Taste, 26
_Theraphosa leblondi_, 94
Theraphosidae, 25, 87-104
Theridiidae, 33
_Theridion_, 3, 23, 32
Thomisidae, 33, 52
Touch, 27, 101, 102
Tracheae, 6
Trap-door spiders, 89, 94, 98
Trap-snares, 31
Use of spiders, 127
Viscid spiral, 15, 18, 19, 20, 116
Water-spiders, 48-52
Wolf-spiders, 58, 76
Zebra spider, 77
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